oxygen, I hope I'll add a transparency slider in Materials dialog box in version 4.3. But don't hope too much from it, and don't be astonished if you get some Z buffer transparency issues like the ones okh reported earlier in this thread.

okh, when the kind of error you report happens, there must be some helpful trace that appears in the Java console. Could you enable it and report it the trace that appears in the console (some text starting by "Exception in thread...")?

And this you probably know. I (accidentally) opened a URL to the online version on a server and got this:

I'm aware about this message, it should be handled in the final release of version 4.2.