Symptoms

Trying to GIT push to remote repository gets to the following error (in command prompt/terminal)

error: unpack failed: unpack-objects abnormal exit
To http://example.com;
! [remote rejected] HEAD -> master (n/a (unpacker error))
error: failed to push some refs to 'http://example.com'

Diagnosis

1. Single user failed to push to remote repository. See #1 cause and resolution.
2. Multiple users failed to push to remote repository. See #2 cause and resolution.

Cause

1. The local repository may be corrupted. See #1 resolution.
2. Disk space in the server hosting Bitbucket Server is full. See #2 resolution.

Resolution

The following resolution shown are referring to the respective cause above.

1. To verify that the local repository is corrupted, you can clone your remote repository to another new directory and then push again. Running git repack might help in case the local repository is indeed corrupted.
2. If disk space is indeed full for Bitbucket Server, clear them and push again.