This is probably due to an international difference in numeric representation.
In the United States, where LabVIEW was created, and Excel for that matter, a decimal point is represented by a period. A comma represents a visual separation of every magnitude of numbers, for example, they are found to identify 1000, 100000, etc, as 1,000, 100,000, etc.
There is probably some miscommunication going on between LabVIEW and Excel. I would suggest that you probably need to replace the comma somewhere with a decimal point. I can't advise how to do this, as I don't know of any way to configure LabVIEW for numeric display (my version appears to only support decimal notation.)
Good luck