when I upload ZIP file for the new gallery, i got the following error
IMG_4856.jpg (Error : Unknown file format)
I tried with (WP 3.2.1 & Nextgen 1.9.1) and (WP3.3 & Nextgen 1.9.1), got the same error.
Then i tried with (WP3.3 and nextgen 1.9.0) and (WP 3.2.1 & Nextgen 1.9.0) and able to add zip files with out any issue.
So looks like this issue is related to Nextgen 1.9.1