If you encounter problems with the SmallPort driver not working occassionally, you might want to try the following, that I found on the following website:

http://www.qsl.net/om3cph/dds/lpt.html

On nonstandard program closing it is necessary to to release driver manually (it was found by debugging under IDE). 

It is done by manual deleting registry key and restart of the system: 

Windows 95 and 98 
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\VxD\SmPort 

Windows NT 
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SmPort
Note: To create and release device in the Windows NT system you must have administrator rights.
