Background

• Windows Active Directory Domain with Server 2003R2 and 2008R2 domain controllers
• Windows XP Pro and Windows 7 Pro workstations

Issue

Some Windows 7 workstations are very unstable. Various applications frequently hangs. Often is not possible to kill not responding process in a task manager. Trying to reboot, machines hang while logging off, leaving user with the only option to power off.
Microsoft Office (Outlook, Word, Excel) seems to be worst affected, but it could be because it is was the most used software in the office.
Windows XP machines were not affected.

Solution

It wasn’t an easy problem to troubleshoot. No errors or warning in the event logs, computers completely unusable.

While trying every possible thing I could think off, I removed all printers from one of the affected machines (all printers were network printers shared from a print server). To my relief this immediately fixed the problem. Double checked versions of all print drivers on the server and all of them seem to be compatible with Windows 7. By reinstalling printers one by one I quickly found that the issue was caused by Nova PDF 7.1 Server Edition.

NovaPDF is one of those virtual PDF printers which allow to convert any document into PDF by “printing” it with a virtual “NovaPDF” printer. This particular (server) version was hosted on a Server 2003 print server and installed on client computers as any other network printer.

NovaPDF website states that since version 7.0 their software is “Fully compatible with Windows 7”, but in this instance it wasn’t the case.

Upgrading NovaPDF to the latest 7.5 version resolved the problem.