Why one tfs build summary shows test results on one machine, not on another

I have a tfs build and some unit tests. Build runs, test runs on build server. But: On one machine I can see test results, not on another. See screenshots. (Ignore the failed tests, there is no test results thats the matter)

The same is on the web-UI: with one user account I can see "test Results" ans stats, on another machine (with another useraccount) there is a message "Test result with ID 123 not found or deleted".

I event don't know where the Test Result file might be located. Is there a permission problem?