Linked Excel sheet replacing cell content with '-1'

Dear friends,

I linked an excel file in my Indesign file, but some explicit cells don't import correctly. The selected cell gets replaced with a "-1" in my Indesign file.

I have no idea why this happens and how to solve it. However it is fixed when I import it as a formatted table, but I need to remove all the style to fit it to the corporate identity.

Thanks already,
Luk