Attempting to redefine a dtd shelf item that is currently in use.
#6129 Run-time catchable error
Attempting to redefine a dtd shelf item that is currently in use.
Additional Information
For DTDS Shelf item 'x'.
or
For DTDS Shelf key 'Z'.
Explanation
It is not allowed to redefine an existing dtd shelf item while that
DTD item is currently used for parsing a document.