Not sure if this is a Firefox, Sandboxie, or HP problem, so I'm dumping everything I know in hopes something will ring a bell: After printing a several Web pages (or some combination of events I haven't identified), Firefox (vs. 45.0.2, but it's happened over several recent versions) running in the default sandbox (Sandboxie registered vs. 5.10 64 bit and probably a couple of previous versions) under Windows 7 SP1 (64 bit) will suddenly refuse to print to my printer (HP Color Laserjet M553 through its 64 bit PCL 6 driver vs. 13.20 -- this version has not been changed). There are no error messages associated with this failure; but after it happens, closing Firefox usually does not clean up after itself but leaves the sandbox full of junk. If I then manually empty the sandbox and then re-start Firefox (sandboxed), the problem is corrected for a while. (I never run Firefox outside the sandbox except to install updates.) Often this problem occurs when I try and fail to change printing "shortcuts," for example from two-sided to one-sided. Either I see the message quoted in the subject line and I am unable to print at all, or I am simply unable to change shortcuts although I can still print with the default. I think this problem may be caused by Firefox because printing from other applications (not inside the sandbox) is not affected while Firefox won't print. Any suggestions as to where the problem might lie would be appreciated. -- jclarkw