Hi Divya, thanks for the answering again.
I think i found out whats going on.
U used the small demo app i provided on your machine, having no problems.
I sent the Excel tile to a US collegue, he got the same problems.
So, its not Excel or any Excel version, its the file.
The difference is the locale, in my thread/app where i cteate the XLSX i had a locale of "de-DE", you had maybe "en-US".
So i changed the Culture of the thread generating the excel to US and the file can be opened without problems.
Obvioulsy a "," , "." decimal sign thing, but still not quite clear why, the cell values are doubles anyway.
So i found something, but have to rework, my localized text for column headers and so on.
Thanks for the help.
Thomas