I don't know what went wrong, but i was getting an error message. So I restored the last version (1.2.4.) and I'm still getting an error message:
Fatal error: Call to undefined function: register_filter() in /home5/inamarrc/public_html/odysseas/zp-core/plugins/filter-zenphoto_seo.php on line 11
Thanks for your help!

Why would you be upgrading to 1.2.5 when the current version is 1.2.6 and has been out long enough that it will be replaced tomorrow with version 1.2.7.

Anyway, your problem is that you did not properly upgrade all the files of the release. Please note carefully that the install instructions suggest you delete all the files from the older version and then upload the new one. This is precicely to prevent you having mixed version files which will assurely give problems such as you encountered.

I suggest you obtain the nightly build and properly install it. The build that will be generated tonight will be the same as the 1.2.7 release so you do not necessarily have to wait for that to be completed.

Thanks a lot for your reply! I did not upgrade myself, I used the upgrade tool in Bluehost. I will try to do the installation myself with the new version today.

Well unfortunately, we have nothing to do with any of these third party install tools, so can be of no help if they go wrong.