You might have seen this error before in the Windows event viewer. However, even if you haven’t seen it, you still might (if you upgrade MySQL). Below is the full error you might find:
The reason is that in MySQL 5.0.41 libmysql.dll cannot be dynamically loaded on windows. The symbol USE_TLS is no longer defined in the Windows build. Windows is expected to allocate the storage for THR_KEY_mysys in mysys/my_thr_init.c using the pthread_key macro.
How to fix this? Downgrade to MySQL 5.0.40 or 5.0.37. You can find them by simply pasting the download URL of the current build and changing the numbers. They always leave old builds on the FTP server.