Gallery Upgrade 1.5 to 2.0.x
From White Helmet Wiki
process Additions:
Step 7, configuring Gallery to recognize domain.com/g1 required some additional steps: check your httpd.conf for
<Directory /path/to/gallery> AllowOverride Options FileInfo </Directory>
You'll need to update this for g1. I added a separate entry as gallery2 will live under /gallery