Assembly must contain algo type

One of our vendor indicators will not install onto cTrader 4.2 and above, it was working fine with CT 4.1, but the following error occurs.

They also have a compiling issue.

CT0002: Assembly must contain algo type

Any help would be good.

RE:

The problem is solved.

In this case, it was class defined as "internal" instead of "public" that seems to trigger hide the information in the assembly.

Best

Carsten