I did it!!! It wasn't the newest Beta version though, I managed to solve the problem before it came out. To be honest, I'm not quite sure, how I did it, but one thing is certain: The cause of the problem wasn't the TLB, it was my Windows taskbar. It was a mess. (Well, acutally it still is). So here's what I did.
I made a completely clean, fresh Win XP SP2 installation onto another hard drive, then installed TLB. I exported a large part of the Windows registry, then imported it into my old system's registry. I didn't really think it would help, but I was pretty desperate. And it did the trick. TLB is working fine since then, I just have to make sure I never turn it off. I did it once accidentally and it's gone. I never was able to switch it back on, so I had to reset the system, not allowing Windows to save its settings.
After tampering with the registry I've encountered a few minor problems in Windows, but they were easy to solve. My taskbar however is still weird. Among the toolbars there's one Free Launch toolbar, which I uninstalled long ago and two True Launch Bars, but only one can be checked. But the important thing is that it's finally working so I'm very happy about it.
I want to thank all of you guys for the efforts to help me out here!