We are using TeamCity 9.1.7 (build 37573) recently upgraded from 9.0 and no have this issue before.
Now we have problem:
[12:59:51][Step 2/5] Unknown data processor type 'mstest' in service message 'importData'
[12:59:51][Step 2/5] ##teamcity[importData type='mstest' path='C:\TeamCity\buildAgent\temp\buildTmp\mstest_results_1463565464803.teamcity.trx']
Could you tell what we need to check and change?