DataFormat.Error: We couldn't parse the input provided as a Date value.

Hi, 

I am working with a dataset retrieved as a xlsx extract of our reporting tool. 

I used PowerBI Desktop for 3 months now and it worked great.

One of the calculation that I do through queries is a Group By.

Indeed I ask for the Sum of Scoping submitted group by Time Stamp (time stamp is only the day of the scoping submittion in our reporting tool). 

1st question: Do we agree that the problem is on the Time Stamp field ? if not ? where does it come from ? 

2nd question: I have tried to change the data type of the Time Stamp field, then of the Scoping submitted field; I have also tried to re-upload my entire data set and re-write the query... 

What can I do to solve my issue ? 

Thanks in advance,

Chloé.