1）In your aspx page，there should be something like UpdateParameters，please set DefaultValue="" for all the strings，and set ConvertEmptyStringToNull=True。
2）Check whether you've set DataKeyNames for GridView，or DataKeys for other controls like Repeater or something else。
3）Converting the Update to TemplateField，and then handle GridView_RowUpdating，plz use something like e.Command,e.Parameters to debug to see what's happening……
Decker Dong ...
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Re: Unable to update a field that has a NULL value
Feb 23, 2012 12:42 AM|LINK
Three suggestions for you Lupin-III：）
1）In your aspx page，there should be something like UpdateParameters，please set DefaultValue="" for all the strings，and set ConvertEmptyStringToNull=True。
2）Check whether you've set DataKeyNames for GridView，or DataKeys for other controls like Repeater or something else。
3）Converting the Update to TemplateField，and then handle GridView_RowUpdating，plz use something like e.Command,e.Parameters to debug to see what's happening……
Reguards！