I am facing the same problem.
Yesterday also and even today.
I think they have not updated/integrated their systems properly or there is any other error.
When I input my registratiom number i.e. PANEM001 it shows that it is not correct or invalid.
I HAVE SAME PROBLEM IN 2 PARTY OUT OF 10 FOR GST TRANS-1, BOTH HAVE IEC CODE, DOING IMPORT EXPORT, SO I THINK ONLY THOSE WHO HAVE IEC CODE THEY HAVE PROBLEM, NEED TO CONTACT DEPARTMENT ASAP.. THANKS
Even i have iec and i am facing the same issue.
But i have already filed my Tran-1.
Lets see what happens, i think gstn and other tax systems arent properly integrated.