When testing FM server7 I try to open a database on the machine I developed the solution with the right password that should give me full access to all the files. But when launching the database on my machine I can't get in with the account/password I use all the time when developing. Shouldn't I be allowed to do so?

Check the permissions of the database file on the server, they must be set to allow fmservd to read/write. Click on the database file, get info, permissions detail.

Permission was not the problem. It seems to me that you are just allowed to have 1 account with full access...

Stevie.at, server 7 has two ways to authenticate users. One is from the FMP file only or windows domain and FMP users. If during your configuration of server 7, you selected the "Filemaker and external server accounts" then you will have to have that user account on that server as well as on the FMP DB you are hosting. Go back and redo the the security wizard and see if that helps.