Sent an email to the HTC support team and received the following reply on this issue:
I have seen this happen before on a few other devices, though it is rare. The most common solution to this would be to clear data from the Messages application. Please be aware that this may clear all text messages from the device, so if you have vital information saved in your text messages, you may want to find a third party application to back up your sms messages before performing these steps.
1. From your Home screen, tap Menu > Settings
2. Tap Applications > Manage Applications
3. Tap Messages and then Clear Data
4. Perform a soft reset on the device by removing the battery for five seconds, reinserting the battery, and then powering the device back on
If you are still having any issues, you may need to clear some temporary files and third party applications using the steps below. If you have a lot of text messages saved on your device, you may also want to delete some of these by tapping and holding on the thread or message and selecting delete.
Clear Temporary Internet Files:
1. Navigate to your Browser
2. Tap Menu > More > Settings
3. Tap on the following: Clear All Cookie Data, Clear Form Data, Clear History, Clear Cache.
4. Soft reset your device by removing the battery for five seconds, reinserting the battery, and then powering the device back on.
Delete Third Party Applications:
1. Navigate to Home > Menu > Settings > Applications > Manage Applications > Menu > Filter > Third Party Applications
2. Uninstall any applications that you downloaded just prior to getting this error.
3. Uninstall any applications that you do not use
4. Soft reset your device again by removing the battery for five seconds, reinserting the battery, and then powering the device back on.
If you are still experiencing this issue, you will need to perform a hard reset on your device. Please Note: A hard reset will delete all personal information and restore the device back to factory default settings. You can perform a hard reset by going to Home > Menu > Settings > SD & Phone Storage > Factory Data Reset.
After the factory reset, if you are still having issues you will need to contact our Warranty & Repair department for further assistance. Their number is 877.293.0807 and their hours are 8AM to 8PM EST Monday through Friday.