HTC Incredible :: "Low On Space" Message Even Though There's Plenty Of Space Left

On Sunday I started getting the message "Low on space Phone Storage space is getting low." on the status bar. When I tap it, I'm taken to the "Manage Applications" screen, so it's clear that the message refers to the "Phone Memory," where apps are stored But when I go to Settings > SD card & phone storage here's what I see:
SD Card Total Space: 14.83GB
SD Card Available Space: 6.15GB
Internal Phone Storage Total Space: 6.60GB
Internal Phone Storage Available Space: 6.51GB
Phone Memory Total Space: 748MB
Phone Memory Available Space: 332MB
I've googled looking for solutions and it's obvious that this is a fairly common problem - especially on HTC phones. But the only possible solutions I've found are:
Too many apps are installed & space really is running low
A "bad" app was recently installed causing this error
Clear the cache for HTC Mail and HTC Message apps
Perform a Factory Reset We can rule this out since there is more than 44% of the Phone Memory available.
I didn't install any apps immediately before getting the message, but to be sure I uninstalled the 10 most recently added apps. No luck.
I've gone to Settings > Applications > Manage Applications, but the cache for these apps is already zero. The "Data" for Mail is 2.22MB and for Messages is 812KB.
This isn't fixing the problem, it's just a way to eliminate whatever condition has caused the symptom. But without an explanation of the actual problem I see no reason to think the problem won't come back in another two months.