DataSource Error: Format of the initialization string does not conform to specification starting at index 0

I'm trying to create a dynamic data source while deploying report in Report Server.

I created a data source, and in connection string passing 

"Data Source=lab-" & Parameters!Login.Value & "-" & Parameters!Register.Value & ";Initial Catalog=MyDatabase"

E.g:

Server Name: lab-100-01

where Login=100

and Register=01

I'm getting Error "Format of the initialization string does not conform to specification starting at index 0"

Please let me know how to pass dynamic connection expression in connection string while creating a datasource in report server.

Thanks in Advance!

ZK