There are several causes of this. The fact that it works when you make changes on the server implies that there is nothing incorrect with the SQL Server user that was set up.
It could be that there is a network error connecting from the client to the database server. This can be tested by creating a file with the extension .udl (create a blank text file and then simply change the extension to .udl). Double click on this file and enter the server, username and password and database to connect to. Press the test connection. If this connects successfully then there probably is not an issue preventing connections in general to the database.
One other thing that was seen recently was an organisation whose server was setup as a "." - dot or period. The server had a name which the was used with the udl connection but the server configuration simply added a dot under the data source value. Look in SQL Server Management Studio using the following SQL:
select * from TXTBLOCK inner join TXTSTREAM on TXTBLOCK.TXTSTREAMID = TXTSTREAM.ID where name like 'ZeidmanDeveloment.REAudit.ConnectionString'
This should give you the connection string that was set up. If the data source shows a dot then you should change this to the name of the server. The server itself can recognise the dot but any other machines thing it refers to themselves which would not work.