You are trying to retrieve data from a LDMS data connection, eg by running a query, and you are getting this error:
"Value cannot be null. Parameter name: type"
This is not to do with Data Connection or Query attributes, but rather it indicates that there is a problem with the integration between Service Desk and Management Suite on your system.
The Service Desk Framework, LDMS Console, LDSD Console, and the COM+ objects (if it's 64bit architecture) all need to be installed on the same server for this to work.
Plus, ensure that the Core Server Name property in the Desktop Manager LDMS Connection is left blank.