just an assumption , but :

basically i have two actions in my test method :

- open the database with the dynamic connectionstring

- run a simple count(*) query on a table that contain 3 rows .

also sometimes i have a Network Error (tcp_error)  during my various tests changes .

and like i said it work fine locally.

btw i have fb 2.5 installed on my local machine , but i stop the service when i want to test the embedded version .

also on the web application i set the lock destination directory with some environement variable .

Environment.SetEnvironmentVariable("FIREBIRD", env.ContentRootPath);

Environment.SetEnvironmentVariable("FIREBIRD_LOCK", Path.Combine(env.ContentRootPath, @"fblock\"));

when i run the web application some empty trace files are created on that folder , so the embed lib is found but take a long long time to get 

data from the database or have a tcp_error message .

can you check if my connectionstring is correct please :

 @"Datasource=localhost;initial catalog=h:\fullpath\database.fdb;server type=1;user id=SYSDBA;character set=UTF8;pooling=False;client library=h:\fullpath\embed.dll";

(i have tried lot of variants ....)

the fb version i am using is :

Firebird-2.5.8.27089-0_x64_embed