Re: using try - catch via scripting in Test Complete..
I suppose you mean analyzing call stacks which can be provided in 500 (Internal Server Error) responses by a web server during a load test. If so, TestComplete does not have built-in means for parsing these messages (and I don't think there is another tool which does this, since the task is too specific and the implementation depends strongly on the tested web server). I recommend that you just save response bodies of the corresponding to files and analyze them manually later. It's not a very good idea to process such responses automatically, because situations when they occur are not normal and must be resolved somehow instead of processing error reports automatically.