A network-related or instance-specific error happened while creating a link with SQL Server. The server wasn't found or wasn't accessible. Verify the instance title is correct which SQL Server is set up to permit remote connections. (provider: Named Pipes Provider, error: 40 - Couldn't open a link with SQL Server)

The issue is the database property showing connection string databases as "xyzsqlexpress" ..basically place the same connection string it wil show the mistake as "escape sequence used"()...basically modify connection string as only "abc" it wil give above given error...so please suggest me some solution with this...

"i've permitted remote connection" and what's exactly this instance title?

You have to escape the backslash character:

Should you construct the bond string in code:

"DataSource=xyz\\sqlexpress"

Inside your configuration file:

"DataSource=xyz\sqlexpress"

In case your connection string consists of a backslash (""), you have to double up ("xyzsqlexpress") or escape it with @ (@"xyzsqlexpress").