Returnil Disc Cache Alert

After months of using Returnil in the Disc Cache mode, this is the first time
I have seen a balloon pop-up to the effect that I have available 19MB out
of a Cache size of 1340MB.
Some details:- Session lock on. Light browsing -no large downloads.
Running Sandboxed (Sandboxie).
Restarted and defragged in safe mode for good measure ( the new version
will be a blessing as the cache will be wiped on restart - there is no defrag
possible with this version 200 5007, and I don't see defrag having anything
to do with the Disc Cache being full ). Maybe switch to memory cache
and then back to disc cache might be advisable, I don't know.

Any ideas as to why this happened ?

 

Hmmm
I'm also using Disk Cache since the GAOTD came out a few months ago.
How do I check the disk cache used?

 

Would be a nice feature but I don't think it's possible.
BTW. Forgot to mention - am on Windows XP SP2 not that this
should have anything to do with my disc cache alert.