Ok, that's weird. If I run your script no error at all occurs here using a Windows-version from 2013-05-02. Despite the fact that both series are almost perfectly correlated.
If I use the catch command in my actual dataset gretl does not produce a matrix with three columns holding the point estimates and the CIs. Actually, should gretl generate a three-column matrix if I use the "catch" command in case of excess collinearity ignoring the error, or should it just prevent termination by jumping to the next task?