Test Script results: Error vs Failed
Accepted answer
Leandro,
There is a section in the online info center that summarizes all of the executions states (The link provided is for version 4.0)
This will provide a definition for each state
One other answer
Essentially "Error" means something was not proper in the system to run the test. E.g. Trying to run a test script but it was not found at the location specified. You really can't say that is failed, since it has not been executed. just could not manage to execute it. It is just an example, hope you got the idea