Datetime conversion problems with en-us culture

have encounterd a strange issue on one of my client servers...Windows2003

the culture of the system is English unitedstates and the culture setting in web.config is "en-US".

my webforms are using Convert.ToDateTime("") to convert the string to datetime object..the string inside the function is in "mm/dd/yyyy" format

So,ideally,there should not be any problem as the current culture is "en-us".

 However,on one of my clients machiens the webforms are failing to convert the string to datetime object ..throwing string was not recognised as a valid datetime.

any help to resolve this  would be gr8ly appriciated
...