Why do I get this error "Statement failed, SQLSTATE = 08001"?
You need to add yourself in the Firebird group 

sudo adduser `id -un` firebird 


or always use localhost address in front of db if Server is Classic or SuperClassic 

See the long thread here 
http://firebird.1100200.n4.nabble.com/Fwd-Have-you-tried-firebird-2-5-SuperClassic-from-the-packages-td3053790.html