Here's the fix for it :
https://github.com/osclass/Osclass/commit/cd9f75080f42d681be2e6bce709269073c0bcec2We DID test it, in fact, osclass has passed all our tests (automated tests) which I could assure you tests a lot of things (but of course, not all).
The problem is that our tests are done in the "testing server" which has ONE and only one configuration, one version of PHP, one of MySQL,... so if your version of PHP is different, or your configuration or... then, there's a possibility there's an error on your machine but not on ours. For example, we tested the update functionality in 4 different machines (2 linux, 2macs) and we did not detect it (it didn't happen to us), also, no-one complained about it on the RC version (previous to the stable release). But this is no excuse, the fancybox error appeared also on my setup, so I should had seen it.
A hotfix version is going to be released soon. Thanks for all your support