Microsoft Dynamics Contect Pack - The last refresh attempt failed because of internal service error

Hi,

I’m trying to connect Power BI to my NAV 2016 system and have not been successful in doing connecting so far. I’m using the Power BI web version, i.e. not the desktop version, to connect to NAV 2016.  

I am able to get through the URL and username and password stage but then when it tries to connect to my NAV system I get an error message that “The last refresh attempt failed because of an internal service error.”

Please can someone give me some advice on how to troubleshoot this error message?