Callbacks + Preview don't work together?

Hi,

We recently added callback-support to our multi-tier application
(using sockets,  callbacks between the application-server and the connected
clients)
Now, we have problems with previews in QUICKREPORTS.
Printing gives no problems, but previewing causes an access-violation
in method TPrinterSettings.GetPrinterSettings on the following instruction :
FPrinter.GetPrinter(FDevice, FDriver, FPort, DeviceMode).
Some printer-drivers stop working with the message "Variant array index out
of bounds"

Our configuration :
Delphi 6.0 update pack 1
Quick reports professional 3.5.1
Windows NT 4.0 service pack 6

Can somebody give me the reason or a solution for this error ?

Thanks in advance

Freddy