Did you ever figure out this issue? We're having a similar problem in that some users simply get an error message when trying to "activate later". I assumed it was permission related, so tried the r,w,c, read acl permission setting mentioned above, but to no avail.
The stacktrace we get is as follows:
17.10.2013 14:33:58.513 *ERROR* [10.0.104.75 [1382045638475] POST /etc/workflow/instances HTTP/1.1] org.apache.sling.engine.impl.SlingRequestProcessorImpl service: Uncaught Throwable java.lang.NullPointerException at com.day.cq.workflow.impl.CQWorkflowSession.startWorkflow(CQWorkflowSession.java:796) at com.day.cq.workflow.servlet.InstancesServlet.doPost(InstancesServlet.java:94) at org.apache.sling.api.servlets.SlingAllMethodsServlet.mayService(SlingAllMethodsServlet.java:148) at org.apache.sling.api.servlets.SlingSafeMethodsServlet.service(SlingSafeMethodsServlet.java:344) at org.apache.sling.api.servlets.SlingSafeMethodsServlet.service(SlingSafeMethodsServlet.java:375) at org.apache.sling.engine.impl.request.RequestData.service(RequestData.java:500) at org.apache.sling.engine.impl.filter.SlingComponentFilterChain.render(SlingComponentFilterChain.java:45) at org.apache.sling.engine.impl.filter.AbstractSlingFilterChain.doFilter(AbstractSlingFilterChain.java:64) at com.day.cq.wcm.core.impl.WCMDebugFilter.doFilter(WCMDebugFilter.java:147) at org.apache.sling.engine.impl.filter.AbstractSlingFilterChain.doFilter(AbstractSlingFilterChain.java:60) at com.day.cq.wcm.core.impl.WCMComponentFilter.filterRootInclude(WCMComponentFilter.java:308) at com.day.cq.wcm.core.impl.WCMComponentFilter.doFilter(WCMComponentFilter.java:141) at org.apache.sling.engine.impl.filter.AbstractSlingFilterChain.doFilter(AbstractSlingFilterChain.java:60) at org.apache.sling.engine.impl.SlingRequestProcessorImpl.processComponent(SlingRequestProcessorImpl.java:257) at org.apache.sling.engine.impl.filter.RequestSlingFilterChain.render(RequestSlingFilterChain.java:49) at org.apache.sling.engine.impl.filter.AbstractSlingFilterChain.doFilter(AbstractSlingFilterChain.java:64) at com.day.cq.wcm.core.impl.warp.TimeWarpFilter.doFilter(TimeWarpFilter.java:106) at org.apache.sling.engine.impl.filter.AbstractSlingFilterChain.doFilter(AbstractSlingFilterChain.java:60) at com.day.cq.wcm.mobile.core.impl.redirect.RedirectFilter.doFilter(RedirectFilter.java:305) at org.apache.sling.engine.impl.filter.AbstractSlingFilterChain.doFilter(AbstractSlingFilterChain.java:60) at org.apache.sling.engine.impl.debug.RequestProgressTrackerLogFilter.doFilter(RequestProgressTrackerLogFilter.java:59) at org.apache.sling.engine.impl.filter.AbstractSlingFilterChain.doFilter(AbstractSlingFilterChain.java:60) at com.day.cq.wcm.foundation.forms.impl.FormsHandlingServlet.doFilter(FormsHandlingServlet.java:220) at org.apache.sling.engine.impl.filter.AbstractSlingFilterChain.doFilter(AbstractSlingFilterChain.java:60) at com.day.cq.theme.impl.ThemeResolverFilter.doFilter(ThemeResolverFilter.java:76) at org.apache.sling.engine.impl.filter.AbstractSlingFilterChain.doFilter(AbstractSlingFilterChain.java:60) at com.day.cq.wcm.core.impl.WCMRequestFilter.doFilter(WCMRequestFilter.java:89) at org.apache.sling.engine.impl.filter.AbstractSlingFilterChain.doFilter(AbstractSlingFilterChain.java:60) at org.apache.sling.rewriter.impl.RewriterFilter.doFilter(RewriterFilter.java:83) at org.apache.sling.engine.impl.filter.AbstractSlingFilterChain.doFilter(AbstractSlingFilterChain.java:60) at org.apache.sling.i18n.impl.I18NFilter.doFilter(I18NFilter.java:117) at org.apache.sling.engine.impl.filter.AbstractSlingFilterChain.doFilter(AbstractSlingFilterChain.java:60) at org.apache.sling.bgservlets.impl.BackgroundServletStarterFilter.doFilter(BackgroundServletStarterFilter.java:135) at org.apache.sling.engine.impl.filter.AbstractSlingFilterChain.doFilter(AbstractSlingFilterChain.java:60) at org.apache.sling.engine.impl.SlingRequestProcessorImpl.processRequest(SlingRequestProcessorImpl.java:153) at org.apache.sling.engine.impl.SlingMainServlet.service(SlingMainServlet.java:206) at org.apache.felix.http.base.internal.handler.ServletHandler.doHandle(ServletHandler.java:96) at org.apache.felix.http.base.internal.handler.ServletHandler.handle(ServletHandler.java:79) at org.apache.felix.http.base.internal.dispatch.ServletPipeline.handle(ServletPipeline.java:42) at org.apache.felix.http.base.internal.dispatch.InvocationFilterChain.doFilter(InvocationFilterChain.java:49) at org.apache.felix.http.base.internal.dispatch.HttpFilterChain.doFilter(HttpFilterChain.java:33) at org.apache.sling.i18n.impl.I18NFilter.doFilter(I18NFilter.java:117) at org.apache.felix.http.base.internal.handler.FilterHandler.doHandle(FilterHandler.java:88) at org.apache.felix.http.base.internal.handler.FilterHandler.handle(FilterHandler.java:76) at org.apache.felix.http.base.internal.dispatch.InvocationFilterChain.doFilter(InvocationFilterChain.java:47) at org.apache.felix.http.base.internal.dispatch.HttpFilterChain.doFilter(HttpFilterChain.java:33) at org.apache.sling.security.impl.ReferrerFilter.doFilter(ReferrerFilter.java:238) at org.apache.felix.http.base.internal.handler.FilterHandler.doHandle(FilterHandler.java:88) at org.apache.felix.http.base.internal.handler.FilterHandler.handle(FilterHandler.java:76) at org.apache.felix.http.base.internal.dispatch.InvocationFilterChain.doFilter(InvocationFilterChain.java:47) at org.apache.felix.http.base.internal.dispatch.HttpFilterChain.doFilter(HttpFilterChain.java:33) at com.adobe.granite.license.impl.LicenseCheckFilter.doFilter(LicenseCheckFilter.java:179) at org.apache.felix.http.base.internal.handler.FilterHandler.doHandle(FilterHandler.java:88) at org.apache.felix.http.base.internal.handler.FilterHandler.handle(FilterHandler.java:76) at org.apache.felix.http.base.internal.dispatch.InvocationFilterChain.doFilter(InvocationFilterChain.java:47) at org.apache.felix.http.base.internal.dispatch.HttpFilterChain.doFilter(HttpFilterChain.java:33) at org.apache.sling.engine.impl.log.RequestLoggerFilter.doFilter(RequestLoggerFilter.java:75) at org.apache.felix.http.base.internal.handler.FilterHandler.doHandle(FilterHandler.java:88) at org.apache.felix.http.base.internal.handler.FilterHandler.handle(FilterHandler.java:76) at org.apache.felix.http.base.internal.dispatch.InvocationFilterChain.doFilter(InvocationFilterChain.java:47) at org.apache.felix.http.base.internal.dispatch.HttpFilterChain.doFilter(HttpFilterChain.java:33) at org.apache.felix.http.base.internal.dispatch.FilterPipeline.dispatch(FilterPipeline.java:48) at org.apache.felix.http.base.internal.dispatch.Dispatcher.dispatch(Dispatcher.java:39) at org.apache.felix.http.base.internal.DispatcherServlet.service(DispatcherServlet.java:67) at javax.servlet.http.HttpServlet.service(HttpServlet.java:820) at com.day.j2ee.servletengine.ServletRuntimeEnvironment.service(ServletRuntimeEnvironment.java:250) at com.day.j2ee.servletengine.RequestDispatcherImpl.doFilter(RequestDispatcherImpl.java:321) at com.day.j2ee.servletengine.RequestDispatcherImpl.service(RequestDispatcherImpl.java:340) at com.day.j2ee.servletengine.RequestDispatcherImpl.service(RequestDispatcherImpl.java:383) at com.day.j2ee.servletengine.ServletHandlerImpl.process(ServletHandlerImpl.java:351) at com.day.j2ee.servletengine.HttpListener$Worker.run(HttpListener.java:625) at java.lang.Thread.run(Thread.java:662)
