"An error occurred while creating a message compose window."

[Philipp v.Thunen]

Hello,

I've just started Netscape 6 (yes, I know... but I had to for helping 
someone who uses Netscape 6). Since then, I can not create a new e-mail 
using Mozilla. The following error message appears:
| An error occurred while creating a message compose window. Please try 
| again.
| [
|
| [ O K ]
(Yes, there is a "[" under the message).
What should I do?

TIA,
-Phil