Both installer page and login page blank

[TKeu]

I am running roundcube on my qnap NAS for a while now.
As of today i got a blank login page, i recently had this error after a qnap firmware upgrade, i managed to fix that by uploading the installer folder again and reconfigure the settings by the installer.

But when I try to do the same now, i am getting a blank page when i go to mymailurl.com/roundcube/installer

No error, just a blank page.
What can i do to solve this?
thanks

[SKaero]

Is there anything in the error log <RC root>/logs?