You mentioned that the file in question is Symtdi.sys. How did you identify this , did you analyse the complete memory dump?.
Have you installed all the features of Endpoint. If yes then try keeping only the AV/AS feature and check whether the issue occurs.
How to add or remove features to existing Symantec Endpoint Protection client installations
http://service1.symantec.com/SUPPORT/ent-security.nsf/docid/2008111808135348