Old bug with new face? "Invalid argument supplied for foreach()"

I´ve got this error (that lot´s of forlks have suffered before, I know):
warning: Invalid argument supplied for foreach() in ....sites/all/modules/panels/includes/plugins.inc on line 855.

I´ve searched for this problem, and eureka! found several answers (always pointing to the same patch) so this isn´t news. (1, 2, 3, 4....)

So, why I´m I bothering you guys? Because I think this is a new bug, or at least the very same bug that didn´t go away yet.
Those posts are way before december 2008, and I´ve downloaded 6.x-2.0-alpha3 from 30.12.2008.

So I´m really clueless, and with all this stuff I really mean: please don´t be mad at me if this is a duplicated post, because I´ve already tried those patches, and the error is still there. And the newer version didn´t make them go away.

Please help me :)
Thanks!
Rosamunda

ps. Additional Info: I used to have installed the 5.x version, and I´m trying this in a testing environment, so I wanted to check that the update went ok. So this is a direct upgrade from an old but working 5.x version. I only have there one panel page: the one created by Advanced Profile Kit. I´ve installed last APK version that says it works fine with Panels, in fact, Michelle didn´t release a new version until panels 2 would be "you-could-say" stable enough. After installing and upgrading everithing, this error appears right after install and prevents me from using the module nor APK.

Thanks again!