Hello,
I would suggest you to migrate the SEP to the Latest version of SEP 12.1 RU3.
http://www.symantec.com/connect/blogs/whats-new-latest-symantec-endpoint-protection-sep-121ru3
This is a known issue with the earlier versions of SEP 12.1 RU1 MP1
A Number of Threads having the same issue. Check this:
https://www-secure.symantec.com/connect/forums/unable-export-install-package
http://www.symantec.com/connect/forums/unable-export-package
Here is the official Article on this Issue:
http://www.symantec.com/business/support/index?page=content&id=TECH180445
This issue has been resolved in the Upcoming version of SEP 12.1 RU1 MP1.
SEP 12.1 RU1 MP1 version has been Released.
Check the Release Notes / Fixes below:
Release Notes for Symantec Endpoint Protection, Symantec Endpoint Protection Small Business Edition, and Symantec Network Access Control, version 12.1, Release Update 1 MP1
http://www.symantec.com/docs/DOC5564
New fixes and features in Symantec Endpoint Protection 12.1 Release Update 1 Maintenance Patch 1
http://www.symantec.com/docs/TECH187656
Hope that helps!!