The subscriber's device didn't respond (MS is not GPRS responding) -- the failure is on the radio/device side, not this GTP exchange itself.
Where you see it
In the Cause IE of a GTPv1-C response (Create PDP Context, Update PDP Context…) on Gn/Gp.
What to check
Check radio-side logs for why the device didn't respond -- coverage, device issue, or a prior radio failure.
Check which GSN sent the response: the cause belongs to that node's decision.
Got a trace with GTPv1 cause 196 MS is not GPRS responding? Drop it in the analyzer: it finds the step that really failed first, which node sent the code and what to ask the other side. Captures, test-system PDFs and vendor exports. 5 free analyses a month, no sign-up.