LinkEx trades can penalize your site

[pc]

I just read on gogle webmaster forum (http://www.google.com/support/forum/p/Webmasters?hl=en) that trades using LinkEx can lower or even penalize your site by google.
I remember that i did trade with one of my mainstream blog using this script and after some time PR dropped from 4 to 2 but can't tell if that was because of this trade or something else.

Anyone else used LinkEx trade and notice something?

[A.J. Angel]

You can use LinkEx but when you output the links, choose to not output the text that says the following:

<!-- Output generated by LinkEX (+http://linkex.dk/) -->

That piece of text will definitely get you penalized as it clues Google that you are trading links using a trade script.