Encrypting File System - XP Pro - Errors

I have recently noticed a problem with EFS. When I try to encrypt a file I
get an error message saying -

"Error Applying Attributes"
An error occurred applying attributes to the file
*Filename*
Unknown Error (0x000000x1)
Ignore | Ignore All | Retry | Cancel

I can still access files marked as encrypted, but when I check the
encryption properties of an encrypted file in the Details panel there are NO
users listed as able to access the file, and no recovery agents. But If I
move a file into an encrypted directory it seems to work fine.

Also, on a possibly related point when I use the Run box there is no longer
a list of previously used commands and I have not changed any registry
settings recently.

I have tried System Restore but as I do not know when this problem first
started I don't know how far back to go, although I have tried all the
recent points.

Any Ideas?
Thanks

Gavin