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How many times do you have to use Backspace? Now how many times have you accidentally missed Backspace and hit F12?
On real Acorn (or Iyonix) hardware hitting F12 isn't a problem, you can easily get back to the desktop from the * prompt. However, with VRPC, hitting F12 is catastrophic. There appears to be no way to recover except for killing the process and rebooting (with potentially a lot of work lost).
Why is this? I there any way to recover from F12 (where the cursor blinks in the bottom left corner but won't respond to anything)?

On my copies of VRPC (SE and SA), F12 does exactly the same as my 'real' RiscOS computers (i.e. suspends the desktop and gives a command prompt at the bottom of the screen)

All that needs to be done to exit from the command prompt is to press the return key. The desktop then resumes where it left off.

Incidently, my main application disables the F12 key (and the rest) for the reason you say.

Yes, I know what SHOULD happen, but the reason for my post was because it doesn't happen. In fact I cannot find any key or combination of keys that gets back to the desktop. I thought that if anyone else has the same problem maybe we might find a solution. As you suggest, the first thing to do may be to disable F12 although I don't want to disable Ctrl-F12 as I use that a lot.

It seems that you are having some extrordinary problems. As Soundgrounder says pressing F12 is exactly the same as on a "real" RiscPC (or any other RISC OS machine). You may have something else running under Windows (including a keyboard driver) that's doing something nasty when F12 is pressed.

Yes, I agree something extraordinary is happening. F12 works normally on my VRPC-SE. It only seems to be a problem on -SA (but of course it may not be the cause of the problem).
Given that a forced exit and reboot is necessary and the fact that F12 must be being handled at a pretty low level it seems unlikely I'm going to find the root cause so I intend to disable F12. However, I thought that would be easy but its not. I have various key mapping modules as well as the OS calls but I can't get anything to trap F12. Every redefinition method I know or have tried seems to be at a higher level in the key handling chain than is needed to stop RISC OS going into command line mode. Has anyone any suggestions?
(I don't have time to experiment with writing a utility to claim the KeyV vector and hack at that level - I thought something must exist already).

I suggest that instead of trying to patch the problem under RISC OS, you should try and find out what is really happening. Something running under Windows is probably claiming the F12 key and causing the problem.