There is an issue with Web Service Data Control component when you create a REST Service Connection, because it saves the absolute path of schema file in DataControls.dcx file.
I faced this problem when I tried to open in Windows, a MAF project that I have created in Ubuntu. As the absolute path of schema file was different, the Data Control was empty.
You can fix this error, changing the SchemaLocations to relative paths in DataControls.dcx file.
To avoid this error, you can change the SchemaLocations when you create the Data Control.