UNIX memory problems w/Progress DB

We are currently running HP-UX 11 as our database server. The database is Progress version 9.1C.

As of late, some of our batch processes that run on the UNIX db server are erroring out because of what appear to be memory issues(at least according to Progress). The db error messages indicate that either there are too may subprocesses and it cannot fork, there is not enough memory to execute the request, or there is not enough memory to allocate a sort buffer. There does not appear to be a consistent pattern to when this happens. Also, we don't appear to be exceeding swap space.

Not sure what else it could be. If any of you have encountered similiar problems, how did you resolve it? Any and all feedback is appreciated.

-Ed