The issue is documented in Cisco bug ID CSCse10330.
A Catalyst 3750 can experience an unexpected reload of the master switch of the stack of 3750 switches, due to a Debug Exception (Could be NULL pointer dereference) error message. This problem is seen only on stacks of 3750 switches that have IP routing disabled.
The root cause of this crash seems to be a slow memory leak that results in the crash of the 3750 master switch when the memory has been exhausted. In order to verify this, monitor the memory usage on the switch.
A possible cause for a memory leak when IP routing is disabled is documented in Cisco bug ID CSCsc59027.
For a workaround:
Enable IP routing with the ip routing global config command and reload the switch stack.
The bug is resolved in Cisco IOS Software Release 12.2(25)SEE2 or later, which can be downloaded from Cisco Downloads.