The PDF print from AJAX worked fine last week. We have not made any configuration change.
The only thing I see is a recent problem with a user that has launched a report without filtering before (report loop over a field). This print has generated a RAM overload (35000 page to generate) and we have to restart the service to restaure the server availability.
EDIT: We found the following error in Event viewer - Application Log :
Faulting application name: QVS.exe, version: 11.20.11922.0, time stamp: 0x5194a88f
Faulting module name: drvui30.dll, version: 188.8.131.52, time stamp: 0x47b190cc
Exception code: 0xc000041d
Fault offset: 0x000000000006661b
Faulting process id: 0x8d8
Faulting application start time: 0x01cf323370fd4ed1
Faulting application path: C:\Program Files\QlikView\Server\QVS.exe
Faulting module path: C:\Program Files\Tracker Software\PDF-XChange 3\pdfSaver\drvui30.dll
Report Id: a3bdf947-9e31-11e3-91f4-e61f13e7236b