A problem has occurred with filesys.exe

So, there I was happily coding away on my Windows Mobile 5.0 Pocket PC project. I made a small change to the code, pressed F5 and suddenly BANG, it stops working. I get an error on the emulator entitled "A problem has occurred with filesys.exe", and visual studio tells me that it has lost communication with the device.

Oops I thought, VS has got it's knickers in a twist and needs to be re-started. No joy. Soft re-set the device. No Joy. Reboot my dev machine. No Joy. Now I'm becomming a little frustrated. Hard reboot the device. No Joy.

I tried all sorts of combinations of actions, but what finally worked was the following....

Delete the source code from my local machine (It's in source control still though!)
Close all programs.
Uninstall the Windows Mobile 5.0 Pocket PC SDK
Uninstall Active Sync
Restart the machine.
Install Windows Mobile 5.0 Pocket PC SDK
Install Active Sync
Restart the machine again
Get the source code back from source control
Open my solution
Run the project

And Hey presto - it's working again.

I have no idea what went wrong, and quite frankly I don't care! It works again and as long as the episode is not repeated, I'll be happy for that.

If anyone can shed any light on the problem however, i'd be interested to know why it happened, and more importantly what can be done to prevent it happening again.