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. A reboot is required for the change to take effect.
The specific registry entry is:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\SubSystems\Windows
That is a long string value. In the middle of that string is SharedSection=x,y,z, where x,y,z are three numbers. In general, the third (z) number should be 2048 or 4096, rather than the much lower default value provided by Windows. Take care not to change any other value.
Here are some Microsoft articles related to Windows desktop heap allocation.
http://support.microsoft.com/kb/184802
http://support.microsoft.com/kb/126962
Below is a link to an article with more details about Windows heap and Unform.