nodecomment_render output empty

Hi

I am getting my node comments in this way

$output .= nodecomment_render($node);

which worked perfectly well. But one day when testing, the comments didn't show up anymore. I was debugging the function and found out that everything is rendered correctly till line 1054

$output = theme('comment_wrapper', $output, $node);

There all the output is more or less swallowed... only the header "comments" is returned.

I checked that $node is filled with the one I selected and $output also has the comments (as html code) before line 1054.

I don't know what I am doing wrong or better what I've changed to cause it ... hope that somebody of you could help me!

Many thanks!!
Eduard