Due to other circumstances, the physical size of the non-virtual CBS Heuristics index (IXX1006) needed to be enlarged and switched to a different, larger data set.
Attempt to then run DBUTLTY to rebuild the index via RETIX failed with RC 46.
RETIX failed with RC 46 since base 1006 was open in MUF via the MUF startop option CBS specifying the heuristic-dbid 1006.
The situation was resolved by restarting the MUF with startup option LIMITED_INSTALL_MUF which enabled MUF without opening some system databases.
This allowed RETIX to run.
After RETIX, the MUF was recycled again with out LIMITED_INSTALL_MUF to return to desired functioning.