This is hard to say based on the information provided. If others can upload it's probably permissions however it could be other things maybe even a bug. To quickly find out please have one of your company's supported users open a new ticket with firstname.lastname@example.org with the pertinent information:
1. User email for user trying to upload image. 2. Step by step directions on flow being followed. 3. Explanation on expectations vs what is actually happening.
We are looking forward to hearing from you soon.
Mihnea Docea | Technical Support Rep, Customer Care | Customer & Employee Experience | Adobe | (:: 1 (800) 497-0335