BSYR417E Invalid Value - Please enter an "S" if you would like to process only this IMS subsystem, an "A" to process all subsystems in the datasharing group or "L" to process only subsystems in the datasharing group that are currently running on this MVS LPAR.

Explanation
An invalid value was entered in the Process Datasharing
Subsystems field. 
User response
Enter a valid value as described in the message text.