Sounds to me you are using local access to the database, either in the
IDE or when running the program (or both).
Does the connection params contain a hostname or ipnr? If not, it's
probably a local connection. In that case only one process can connect
to the db. The IDE (connection component) may be stay connected, so when
running the program you get this error.

John

Op 20-12-2018 om 12:00 schreef Alan J Davies
Alan.Davies@... [firebird-support]:

> Hi I use FB3.04 and Delphi for writing the front-end programs. I had no
> problems with FB 2.5 for years, but now I've upgraded I have problems
> every time I run a compile and run cycle.
> I get the error - "Error while trying to open the file - the process
> cannot access the file because it is being used by another process."
>
> The file in question is the database so I have to close the database
> every time I make a change which means I cannot check what's going on in
> the event of an error. Then everything works perfectly.
> This did not happen with FB 2.5
> Is there a setting or something similar in FB to allow this?
> The OS is Windows 10, 16GB, SSD drives
>
> Thanks
> Alan