Go and look at all the profiles you have assigned and add up the "Maximum Cache sizes" from the config. That's the figure that you are using actually using per-TMM.
I assume you have seen this http://support.f5.com/kb/en-us/solutions/public/12000/200/sol12225.html?sr=11064657
Check your log for the error message - if you can't find it as you have lost the logs try updating the profile that didn't allocate (just change one thing) and save - you should see the error message then.
Go and look at what you are actually using compared to you Maximum cache size - you'll probably find a few you can reduce the Maximum Cache Size on.