Can't Save As Maya Ascii

[loganb]

just trying to get an ma file out of an mb file...I get this:

CODE
File contains unknown nodes or data.  To preserve this information, the current file type cannot be changed.

How can i isolate and delete these unknown nodes, so I can get my .ma file?

[gmask]

delete ls -type unknown

actually if you look in the optimize scene file command I believe it has an option to do this there