Hi there,
I am experiencing the same issue & am wondering if I can get some follow-up information. When I looked into the problem, I checked the workflow class itself using Reflector to see if I could get a better idea of what it was doing under the hood, and it appeared to be keying the date format off the SPWeb.Language property. This seems to be LCID 1033 (en-us) and I couldn't find a language pack for any other English language.
I'm at the desperate end of my rope. Would you be able to explain more about setting the region for the service account running the timer service? We currently have it set up as a domain account. Are you talking about regional settings in AD?
Thanks in advance,
Andrea James