AEM unable to login

Hi Experts,

We are running AEM 6.0 with SP2. After a recent restart of one of our publish instance, we are no longer able to login with admin credentials.

We keep getting the following error in the logs:

16.10.2015 13:49:40.262 *WARN* [qtp2074601335-30] org.eclipse.jetty.servlet.ServletHandler /libs/granite/core/content/login.html
java.lang.IllegalArgumentException: Invalid token ''
        at org.apache.jackrabbit.api.security.authentication.token.TokenCredentials.<init>(TokenCredentials.java:42)
        at com.day.crx.security.token.impl.TokenAuthenticationHandler.createCredentials(TokenAuthenticationHandler.java:578)
        at com.day.crx.security.token.impl.TokenAuthenticationHandler.extractCredentials(TokenAuthenticationHandler.java:352)
        at org.apache.sling.auth.core.impl.AuthenticationHandlerHolder.doExtractCredentials(AuthenticationHandlerHolder.java:75)
        at org.apache.sling.auth.core.impl.AbstractAuthenticationHandlerHolder.extractCredentials(AbstractAuthenticationHandlerHolder.java:60)
        at org.apache.sling.auth.core.impl.SlingAuthenticator.getAuthenticationInfo(SlingAuthenticator.java:697)
        at org.apache.sling.auth.core.impl.SlingAuthenticator.doHandleSecurity(SlingAuthenticator.java:452)
        at org.apache.sling.auth.core.impl.SlingAuthenticator.handleSecurity(SlingAuthenticator.java:438)
        at org.apache.sling.engine.impl.SlingHttpContext.handleSecurity(SlingHttpContext.java:121)

Any help in this regard is much appreciated !!!

Thanks,

Anwar