Connection with database

do you try it directly without app.config file?

if yes then write the result,,is it working or not when you put it direct in your pgmm,
write the code that you are using ..

Thanx pankaj bt when i use
Data Source=(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(HOST=MyHost)(PORT=MyPort)))(CONNECT_DATA=(SERVER=DEDICATED)(SERVICE_NAME=MyOracleSID)));User Id=myUsername; Password=myPassword;
this code in my app.config file it gives me
error:Object reference not set to an instance of an object what should i do???
:(

try one of these

Using TNS

 
Data Source=TORCL;User Id=myUsername;Password=myPassword;

Using integrated security

 
Data Source=TORCL;Integrated Security=SSPI;

Using ODP.NET without tnsnames.ora

 

Data Source=(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(HOST=MyHost)(PORT=MyPort)))(CONNECT_DATA=(SERVER=DEDICATED)(SERVICE_NAME=MyOracleSID)));User Id=myUsername;
Password=myPassword;

check below link:

http://docs.oracle.com/cd/B28359_01/appdev.111/b28844/using_aspnt.htm#autoId0

 download it:

http://www.oracle.com/technetwork/developer-tools/visual-studio/overview/index.html

mark it as answered if its help you.