I was converting some textures of weapons in Asset Manager then I was checking in Tom BMX Xmodel Utils and I watched a very weird problem in a texture which I had never before seen. I tried to reconvert the texture and this message is shown

now I cant use asset manager, I tried with anothers .gdt but the same problem is shown.
Any solution or idea that is not to reinstall mod tools?

There must be a .db file somewhere in mod tools which fucks up the converter when it is corrupted. I can't remember its name or path since i don't have my computer with me but all you need to do is delete that file. It's just an sqlite file that contains asset info and its name probably has something to do with the word "asset".

Yes I had this before, you need to go to root/assettgtcache and delete the 'converter.db' file in there.

Thank you very much JohnDoe and Stevie!  it worked.
Both answers were correct.