I’ve had this problem periodically myself. The good news is that Benji built in an easy solution.
After launching the program, instead of logging in, click the ‘Debug Tools’ button in the lower-left corner of the screen (it looks like a wrench). From there you’ll get a new window warning you about possible locally-cached data loss, as well as a ‘Clear Local Cache’ button. Click the button to purge the local cache and re-download all content.
IMPORTANT NOTE #1: I’m just a Shaxpir user like yourself so take my advice with a grain of salt.
IMPORTANT NOTE #2: Whatever you do, don’t try clearing the local Shaxpir cache files through Windows Explorer. Use the method described above. A while back I tried to be slick and clear the cache manually through the file system and ended up blowing away ALL my data (thankfully Benji was able to restore it all for me, but it was scary all the same).