WorkspaceId must be a Guid object. Please select a workspace you own and fill its Id in web.config

Hi, 

Can anyone help me with this.

I have opened the web.config file in visual studio. The file comes from a power bi developer example file.

I have changed the 5 things it asks. I run the file but everytime i do and then click on Embed report the following comes up: 

WorkspaceId must be a Guid object. Please select a workspace you own and fill its Id in web.config

I have put this in with just numbers, reports/ groups/ and just / and never works.

Can anyone help ?

Thanks

Anthony