IMCE stops uploading image in the middle of uploading
I cannot find the string "A file with the specified name already exists" anywhere in the source of IMCE 6.x-2.2.  

Looks like the same issue was noted here on Drupal.org and was not part of IMCE

I would recommend updating to the newest version of IMCE in the 6 series to see if this fixes the issue. (Currently 6.x-2.3)