did u edit the config.php and made any changes for thumbs , like the resolution size ?

The resize function is not working at all. You should enable debug (go to config.php) and paste the errors and warnings.
Regards.

The thubms are created with the resize function. This function is the same that chevereto uses to resize full images when you input some width... So, is something with imagecopyresampled and stuff like that.

It's hard to tell more if you can't output the debug. When the script upload a remote picture, it opens a curl transfer and copy the image in the work folder. From this point all the process is the same for both local and remote.

So... If the script can upload remote pictures it means that you probably touch some in the source code or is the most weird issue ever... This seems to be not a curl issue... Sometimes when I upload from local with resize works 100%, %50 (just the image) or 0% (black image and thumb). Thats why in my first post I say that it was a resize issue.

Mmmm did you change something about the random name generator? I'm sure you did.
Because that is the only clue. You change the random name generator (in bad way) and the script can't find the proper image to do is job. That is why sometimes work, because mantains the image name and in the other hand it changes the name.

Edit: I just look the new one and it's the same thing =/

Ok, iI think that i got it!

When you upload a remote picture (new or old install) you can see that sometimes the uploaded file is incomplete... Meaning that the curl transfer is shutted down (probably by your hosting company or php settings). So I try to upload a very little file.. Like 1kb and there is also errors, the host just don't accept the transfer.

The resize will always fails if the image is corrupted or incomplete, so... there is your problem.

Fix? You can allways use another hosting company. If the server is managed by you (I mean, vps or dedicated) you should config the curl library.