Many thanks to all who helped me solving the problem with my smeary
I promised to tell the solution on the net and now here it is!
It was, as many people suggested, a problem with the primers! After I
run several control reactions to veryfy that, it was finally clear.
My primers were responsible for the smear. Identical primers obtained
from another company gave very good results with the same methods
used before so we could blame it on the supplier. They agreed to send
us the primers again, this time HPLC purified for a -fair- price!
To all who have further questions
e-mail: bergera at rz.uni-duesseldorf.de
Yours (happy now)