Can somebody tell me what is wrong with this code?

Dim rowNew As DataRow
rowNew = gModelTagsDS.Tables("header").NewRow()
rowNew("model") = Trim(txtModelNum.Text)
rowNew("modeldesc") = Trim(txtModelDesc.Text)
rowNew("partdesc") = desc
rowNew("quantity") = temp


I get an Object reference not set to an instance of an object error.

TIA!!

MAC