Did you ever get an answer for this? I'm having a similar issue. I have a date field in a gridview and I'm setting the date in Row_Updating. When I do a This.Save I get the same error. It seems like of the the rows contained null values to start with then saving the DataSet back with the same values shouldn't cause an error.

>There seems to be a general problem where mmGridView.BindBack() causes unhandled exceptions with invalid (mostly null) data BEFORE the business rule check.
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>It seems that the solution is either:
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>1) subclass mmGridView, override BindBack(), and
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>a) do some instance code for each table/gridview's data particularities. Horrible.
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>or b) have some general solution where BindBack() checks nullable and returns some obviously invalid token to be checked in the business rules later.
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>For example, a blank integer where 0 and -1 are valid entries might get set to -999999 as a "set me to DBNull flag" and just hope that value's never a valid entry. Horrible.
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>or 2) manually do data and business rule checks and cancel out before the call to
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>        // Save the DataSet (the GridView automatically binds back)
>        mmSaveDataResult saveResult = this.Save(this.oManualCountSheet, dsManualCountSheet);
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>(But this still wouldn't handle the case where data is supposed to be nullable.)
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>Suggestions please! Thanks!