Thanks again.  Camera Raw version is 6.7.  If I delete this file, how do I replace it?  The updater will not run, even though I am on-line, it immediately says the server is not responding. 

If I hold down Ctrl+Alt+Shft before opening PS, I get a Photoshop Properties window (no reset there), but if I press these keys after clicking on the PS icon, I get an egg-timer for several seconds, followed by.....nothing!

I'm thinking the next move is to uninstall and reinstall CS5 in full, from the disk??

This incident may tip me into buying a new machine.  I'm running on a faithful old Pentium 4 with 2GB RAM, running XP Pro.  Since I upgraded to a Canon 5DII (raw files are up to 30MB) and CS5, it has struggled somewhat, and there is always a delay and progress bar when opening raw files.

Your help is appreciated!

>>A reinstall will not affect the preference file.  It should say "delete photoshop settings?"  say yes

Unfortunately, the short-cut to delete photoshop settings is not working.  In fact, and worryingly, after I try it, PS cannot be opened at all, until I have closed and restarted my Windows session.  However, I can locate and delete the CS5 Prefs (PSP) file and have tried this, but the errors remain.  It does not seem that a corrupted preference file is the problem.

Thanks for getting back to me.  I've made a little progress.  It seems that my usual identity is corrupted, or is being affected by PS crashes, which are crashing the DDE server window and also preventing some other applications (such as Adobe Acrobat Pro 9 and even Internet Explorer) from running in that identity too.  If I close and restart that identity, it's fine again as long as I don't even open PS.

So I created a new identity just to see if PS would run OK there, and it did, for about 4 hours, but then errors started to recur, such as 'PS has encountered an expected problem and needs to close....' when opening raw files.  As I'm trying to finish off editing a set of wedding photos, this is a pain.

I'll try reinstalling PS, but I suspect the problems I'm seeing may be due to a lack of resources.  So, reluctantly, I'm thinking it may be time to replace my faithful and carefully maintained Pentium 4 running XP, and enter the dizzy world of 64-bit.  One issue may be installing CS5 on a new machine, since I only have an upgrade disk, having migrated all the way from a full copy of PS6, via a CS2 upgrade.  I understand that it would be wise to go for Windows 7 Pro, which contains an emulation of XP and therefore allows older 32-bit software to be installed.  Any other points to consider?

By the way, your suggested search for the file 'camera raw.8bi' turned up two versions - the CS5 one, and the older CS2 file.