problems connection to sql server 2005 express from vb.net application

[willow1648]

3 years ago I developed a vb.net application that connect to sql express 2005 data base.
The application worked fine.
We replaced our computers, so we installed the application again. (The same exe file, the same sql server and so on).
Now, only when loading few forms I receive the following message:
“An error has occurred while establishing a connection to the server. When connecting to SQL Server 2005, this failure may be caused by the fact that under the default settings SQL Server does not allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified) “

I followed every direction and open all the needed ports, firewall, sql browser and so on.

Note that when we log in to the application, a connection is needed. The user verifying is working fine; it means that the connection is working properly.
After that a few more forms that pulling data from the data base are also working fine.
Only when I open a few forms I’m having this problem.
The connection is not changing between forms.

I installed the application on 3 more computers and still having the same problem.

Someone can help please??
Thanks in advance.

[Frinavale]

If you have created a 3 tiered application you would just go to the Data Access Layer and check the connection strings and settings there in your application (maybe something got hard coded??)

I am not good with networking, firewalls etc...so the first thing I would do is disable all firewalls on the client and the server to see if this fixes the issue.

Did you reinstall the database?
Check to make sure that the user accounts have the appropriate permissions to use the features that the application requires.

-Frinny