Error: Object reference not set to an instance of a object

Hi.

I have a aspx form which has a tab container and two tab panels... and in each tab panels i have around 7 upload controls and a button. for all of those upload control i have a required field validator...  and since i have two tabs I have given the each control in the Tab panel a different Validation group..

On click of the button i have this code

 Page.Validate("ASC") Then
UploadTextDocument()
and I am getting the above error at dim strAS as stringstrAS = Path.GetFileName(FlAS.PostedFile.FileName)
 
any help will be appreciated..

Thanks,

Karen
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