cropping is suddenly slow in LR2.5

I've been using LR for about 8 months now. I have a Q6600 quad core CPU, 4 gb ram, nvidia G8600, WinXP Pro 32 bit. I have a 500gb hard drive that is only 20% full. I shoot RAW with a 30D and process with LR 2.5.

In the last week one function in LR has suddenly started to lag. When I choose the crop function and either drag the margins to crop or drag a line to correct level the response is noticeably slower. It takes a second or two for the computer to catch up to my mouse movement.

No new software has been installed, no upgrades, no new hardware. I use LR almost every day and suddenly this changes. Has anyone had this issue, know anything about what could be causing this?

Tried defragging the cache drive? With that little ram (maybe as little as 2.5gb if you didn't use /PAE) LR2 will be using disk cache quite a lot.

I've optimized the catalog. I'll try defragging.