Client shared access to a shared folder but user is unable to upload any documents

Hello, 

We have a client that shares a folder with us, the client granted edit and upload access to the user but when the user tries to upload a doc it says "oops unable to upload the file" what could be the issue here? 

Troubleshooting steps below

1.  Tried a machine not restricted by any security controls.
2. Had client send an invitation to another email, user created a new account but was still unable to upload files. The user still seemed tied to her old acount.
3. client gave me access, i was able to upload files with no issues.