I have a very similar if not the same problem. Version 2.2.2 worked fine on my PC (ThinkPad T410 under Win7 Pro 64bit), but after updating to version 3.1.0, printing to the PDFCreator does not work any longer, i.e. each task is only put into the printing queue and then just sits there forever.
I have thus de-installed PDFCreator, rebooted the system and reinstalled PDFCreator, but to no avail. One further idea was then that the problem might indeed be related to the spooling folder (%temp%\PDFCreator\spool), because that was not accessible to me in first instance when I tried to look into it with Windows Explorer, but even after fixing the permissions to be the same as for the %temp% folder itself, the problem persisted.
I have tried to print a test page from the PDFcreator application. There, the PDFCreator testpage works, but the Windows testpage does not. That could, according to your post, be an indication for incorrectly configured permissions of/within the %temp% folder, but then I would have no idea what could be wrong with settings that work with all other problems and even the version 2.2.2 of PDFCreator. Could you perhaps mention how the settings should look like in order to make PDFCreator work in version 3.1.2?
The version number of the pdfcmon.dll in my %windir%/System32 folder is 0.9.7.0.
Thanks in advance
Edit: I have now also tried to completely empty the %temp% folder (thus also erasing all subfolders), set permissions to ‘full access’ for the system, for local administrators and for my own user account (as looked up on another PC). Then started PDFCreator again for debugging and trying to print testpages - with the same result as before: PDFCreator testpage prints out fine, but Windows testpage does not. So, fiddling around with permissions did not resolve the problem for me.