Brian,
Just has same trouble this week:
"
The Windchill Service is not starting when using Java 1.6.18, which is delivered with Windchill 9.1 M050, with no error messages.
Resolution
Reinstall the service using the follwoing ant task:
ant -buildfile <windchill>\opt\ntservice\WindchillService.xml install -DserviceName=<servicename>
Override the default memory allocations by adding the following argument to the ant script:
-DmaxHeap=6 (for 64-bit)
-DmaxHeap=3(for 32-bit)
"
Hope it will help
Christophe