Apparently the version of Android 2.2 which could be downloaded straight from HTC's servers before the over-the-air updates even started wasn't final. To fix any troubles those who downloaded and installed that update may be experiencing, Sprint is rolling out a fix:
This is an OTA package that will upgrade your phone from the unofficial version of the Android 2.2 release (.3 version) to the final production version (.6 version) will be available this evening.
The upgrade package is very small and will take only a couple minutes to download and install.
How to update your phone:
• You may initiate the download on your phone by going to Settings > System Updates > HTC software update or
• The Network will initiate a push to your phone.
This Maintenance Release updates EVO from the unofficial Android 2.2 version 3.26.651.3 to version 3.26.651.6