A CAIRIM S878 can precede a task abend with COMPLETION CODE SA78 REASON CODE 00000004.
ANSWER:
The specified REGION size of 524K for CAS9/CAiRIM execution was too small. The storage request from (IBM) OPEN processing resulted in an operating system getmain failure.
Increase the REGION size on the EXEC Card of the CAS9 proc. Although the default REGION as distributed is 2M, specifying REGION=0M resolved this problem.
https://www.ibm.com/support/knowledgecenter/en/SSLTBW_2.1.0/com.ibm.zos.v2r1.ieae100/regsize.htm