Hi jcl,
thanks for quick reply.
I changed it to
MyMACD = myMAFastLength[0] - myMASlowLength[0];
but I still receive the same error message and assume,
that my vars declarations are the problem.

I tried also this (which works without error message):
vars MyMACD = series(myMAFastLength[0] - myMASlowLength[0]);
..but then I receive same error again for the MyMACD definition.

What is wrong here?
Thanks so much.