set remote access(for all users) to sql server database on local network

EXEC sys.sp_configure N'remote access', N'1'
GO
RECONFIGURE WITH OVERRIDE
GO

ConnectionString=@"Data Source=SERVER\SQLEXPRESS;Initial Catalog=test;Integrated security=SSPI;Persist Security Info=False";  

Also check your sql conenction string. Is it universal or only for your computer. If it is like this;
"Data Source= PC1\SQLEXPRESS;Initial Catalog=DatabaseName;Integrated Security=true;" change the PC1 to "." so others can conenct to it. "Data Source= .\SQLEXPRESS;Initial Catalog=DatabaseName;Integrated Security=true;"