I had the oringinal error message ( "Unable to access UserTransaction in DataService" ) with flex.samples.crm and JOTM, but using tomcat 6.0.16 with a virtual directory.
...And reading this post gave me the idea of a JOTM was not installed...but I was using LiveCycle 3 ES 3 Beta 3 with integrated server (where JOTM is already installed)...
My issue was obviously different becuase I was using docBase in my conf/localhost/<SITE_CONTEXT>.xml
....But tomcat still did not 'see' JOTM installed even though the jotm files are already installed (as part of the installation in ..tomcat/libs) - but if using docBase you need to copy the jotm file into the <SITE_CONTEXT>/WEB-INF/libs/ directory.
I mention it here now, after all this time because someone might find it usefull...and save some hair pulling.
Hindsight in a fabulous thing