This is the exact process that happens when I am trying to upload a mod:
1) make the mod with its image file.
Mod Name: Grombrindal_WhiteDwarf_reskin.pack (Size 1476 KB)
Image Name: Grombrindal_WhiteDwarf_reskin.png(Size 256x256 128 KB)
2) place it in my data folder and test it all works
3) find it in the mod manager in the launcher
4) click on upload
5) The EULA screen pops up I accept
6) the category pop up appears and I select one (I have selected different ones, in case it was something to do with that)
7) the pop up goes away once i select one, now usually the launcher will freeze for a fraction of a second and where the upload button used to be then it is replaced by UPLOADING
8) Now what happens with me is it freezes for a second then the uploading doesn't appear it just goes back to allowing me to select upload again.