Hello Nicolas, and thank you for helping out!
Two questions...
#1 - when you went in to purge the cache, was anything in there? I noticed someone was logged in when I went to update Joomla, so I waited until they logged out. Once they were logged out, I personally cleared the cache, updated Joomla to 2.5.27, and went back to confirm the cache was cleared and I didn't see anything at that time...so hopefully something did not repopulate in the cache.
#2 - Did it seem to you the errors I got when trying to install HikaShop Essentials the first time were resolved with the subsequent re-installation attempts? There's a photo attached to the first post called "Errors"...those would be the ones I'm speaking of.
Thank you!