I know, but that's impossible to do on that server. So the only solution I found so far is to install the application in another computer. But anyway I would like to understand why this is necessary in Firebird. It would be great if anybody knows the answers to my questions of my previous message.

Why do you think the problem only happens with Firebird? Use Google and you will find documents from Microsoft telling to not install MSSQL Server in PDC machines. As I said before, any write intensive application (like RDBMS) will suffer with no cache.