On Windows servers that support many users and many services, it is possible to run out of heap space, a portion of memory allocated to services and desktop users in distinct ways. If a system runs out of heap space, it is possible for jobs to hang as UnForm is unable to launch processes to handle connections and/or jobs.
Heap space can be modified with registry changes. Care must be taken to avoid allocating too much heap, as the system won't be able to start at all, so adjustments should be made incrementally by a qualified system administrator.
Here are some Microsoft articles related to Windows desktop heap allocation.
Below is a link to an article with more details about Windows heap and Unform.