Well, MS Excel will show this message when you have inserted numbers as strings. I think you may try to use an overloaded version of Cell.PutValue method, e.g
Cell.PutValue(stringval, true); //Please specify true for the second parameter (bool isConverted).
Now, the cell would have numeric data and you don’t get the message (“Numbers stored as text”) in MS Excel.
Alternativley, to eliminate this info error, you need to uncheck that option manually in MS Excel. e.g… in MS Excel 2003, click menu option… Tools|Options|Error Checking tab, now uncheck the checkbox i.e…, “Number stored as text” and everything will be fine.