SSH Certificate authentication for i5

I'm working for a customer of us who want to monitor some parameters on his i5. I use SSH to run commands and to extract the results. However I had a problem using certificate authentication. Authorized_users file, certificates, permissions ... everything was done as it must be but I didn't get access. After some debugging I realized the homedir on the i5 had to be in upper case though i5 is not case sensitive.