We have seen this behavior in the past when the test project accidentally included a circular test-as-step reference. For example, Test A is trying to execute itself, Test A, as a subtest. This causes an infinite loop in Test Studio as it loads and scans the test during project load time. Similar if Test A -> Test B -> Test C -> Test A, the same result will happen.
To find and fix this requires a process of elimination. Remove about 1/2 of your tests (or any large count) from your test project and see if it will load. If it does then the problem is somewhere in that 1/2 you just removed. if it doesn't the problem is somewhere in the 1/2 remaining. Continuing removing blocks of tests until you identify the offending test. Once you have identified it you should be able to look at its' steps and remove the circular reference. This may require "hacking" the .tstest file in a text or XML editor since it probably won't load in Test Studio.
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