The numbers at the end of the error messages are line numbers, indicating which line of the feature code is causing the error. You can save the code to a text file from the dropdown menu in the OpenType panel, then open in a text editor and see if the referenced line numbers provide any clues to the errors. If your feature code is limited to kerning, you might also try Tools > Kerning Assistance to check for overlaps or other oddities, then update the kern feature.

You also might see if "Clean up classes" in FontLab catches any issues (first button in Classes panel).

You have the same glyph in more than one kerning pair and FontLab is attempting to fix the problem. You need to review your classes and fix the problem.

Thank you all for your answers I really appreciate it.

I have found that itilde was actually in two classes and delete it which resulted in removing the last error but still "glyph class.." and I'm dont have idea what does that mean.
As for the gargoyle's suggestion, it didn't give me much clue, thanks for the try :) It seems that "m" and "O" are overlapping, but "m" is defined in one class that I have only set to kern on the left side and the other to kern on the right side (im not sure how is this called, but in the classes panel I have checked left box for one class and right box for the second one) so I'm not sure how to set the class kerning right than?

Thanks again for your help

Apparently the "Glyph class ... redefined" error occurs when classes are defined both in the Classes panel and in the lower pane of the OpenType panel. Google turns up a few old threads with more explanation:

http://www.google.com/search?q=fontlab+warning+%22glyph+class%22

Thank you very much for your help, I have managed to get rid of all that warnings, but still my kerning doesn't work in for instance Photoshop CS5? Are there some additional options that I need to check so it would work?

Thanks again for help everybody!

You need to limit the kerning to something simple, make that work, and then build it up again. Save a copy of your font and delete all of the classes. Then start adding them and testing them, one class at a time, until you understand how to build working kerning classes. Then go back and fix the original font.