Cannot convert date (which is in text format) to date in numeric format

Hi all,

I have a curious problem with dates in excel. I read the other Q & A on the topic of cannot group in pivot table couple of hours ago in the forum and got some ideas and applied them all to no avail.

Problem: The issue is that the dates are in text format. I want to convert them to dates in numeric format so that I can apply the grouping. But whatever I try it does not work. I am attaching the excel file.

column c: the dates which are in text format
column d: i checked if they are in text format using the function isnumber()
column e: I get an error Value# upon applying the datevalue() function to change the date into numberic format.

Please help. Many thanks in advance.

Regards
gp