It seems like AOLserver is not executing the tcl scripts. AOLserver should never be sending the content of the tcl script to the browser. It is very strange that it only happens occaisionally.
I suspect it is not a mime type issue, since the tcl should never be sent to the client under any mime type. It is more likely that the problem is in your modified OpenACS.
BTW, it would be very interesting to see what parts of OpenACS you are using.
