First, copy from FB install files (after download from firebirdsql.org) zip kit for manual/custom installs win32 or x64 after unzip this file for using with your project (usualy to directory with app exe file):
\plugins\engine12.dllfirebird.conffbembed.dllib_util.dllicudt52l.daticudt52.dllicuin52.dllicuuc52.dll
and after edit firebird.conf
#Providers = Remote,Engine12,Loopback
change to
Providers = Engine12
