Craig,
Did you check previous discussions on negative cache error?
Have you cleared all of the caches ...
/UI2/INVALIDATE_GLOBAL_CACHES
/UI2/INVALIDATE_CLIENT_CACHES
/UI2/NWBC_DELETE_MENU_CACHE
/UI2/PAGE_CACHE_RESET
/UI2/DELETE_CACHE_AFTER_IMP
/UI2/DELETE_CACHE
/UI2/CHIP_SYNCHRONIZE_CACHE
Transaction: /IWFND/CACHE_CLEANUP
Transaction: /IWBEP/CACHE_CLEANUP
You seem to have a custom theme. We have had a similar issue and when nothing worked, took the custom theme out, set it to blue crystal then it worked. We then set the custom theme back again everything was fine. Give it a try if nothing else works.