This could be as a result of a long test run when the execution results size became too high. Try decreasing the amount of information you post to the Test Log.
BTW, a couple of similar problems have been fixed since the time TestComplete 5 was released. So, using a newer version could probably fix this for you.
Since TestComplete 5 was released long ago, we will not be able to provide you with a fix for this version even if we determine the cause of the problem.
Anyway, we can investigate the problem and try to propose a workaround. To help us with this, please collect more information about the problem: