I guess that's a different problem, I just realized you are on Win2000 so that's probably the culprit. I believe it requires at least XP.
All TAP files that were dumped are available in either the TOSEC set or the Pale emulator. A couple of bad dumps there though not all of them properly tagged.
'Play TAP' was added specifically to make the emulator frontend friendly and also much easier for users who don't know the system, the other loading methods will work in real time. This automated loading is great and something that should be available on MESS at least to some extent, tape loading on MESS is a pain and makes it unusable for any frontend integration
If you are thinking on looking at the source code you might want to wait until the next version since Jonathan is going through some important changes right now which should make it more accurate.