Deployment changed in winter 15' introducing testLevel, make sure you are setting it to NoTestRun, They might have changed the default level as in winter 15' it was set to NoTestRun but this could now have changed. Check your deployment and validation routines.
Critical Update in the Winter '16 Release
Who is impacted by this?
Any partner whose org contained tests with callouts or calls to getContent before our recent Winter '16 patch release (patch 198.7).
What is the change?
After a recent Winter ‘16 patch release, customers and partners may be seeing the following error message when running a test that attempts a callout or calls getContent, “Method defined as testMethod do not support web service callouts, test failed”.
Why is this change happening?
Prior to this recent change, tests using callouts/Pagereference.getContent() were marked as "skipped". However, these tests NEVER worked, but never failed either. Deployments were allowed to proceed without fixing these tests.
As of patch 198.7, this behavior has been changed, such that these tests are now correctly marked as "failed" when executed.
What action do I need to take?
If you and your customers are experiencing this, here are two recommended workarounds:
Remove or comment out the tests that were previously being skipped. Please note that since those test classes have always been skipped, commenting them out now will not affect the other test classes nor reduce the testing done on the application upon deployment.
Implement HTTP Callouts by implementing the HttpCalloutMock Interface. See this article on the Developer site for more information - https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_classes_restful_http_testing_httpcalloutmock.htm