X'10DC' CAN'T FIND SYS EXT SEGMENT MSGSISEX

Explanation
 The message flag indicates that the SYS EXT prefix
segment is present, but the segment cannot be located.

Programmer response
 Locate the message and verify that
flag MSGESEX or MSGETMR is set. If it is set, then a SYS EXT prefix
segment with a code = 8A hex must be present. This is an internal IMS error.