>> Are you playing with Grid's rowsource or trying to change Datasession?
>>this could blank out grid's definition
>>
>>Bye
>>Jayesh
>
>Nope - the grid isn't really blank (as you get when the data source goes away) - all i'm doing is calling a simple UDF, which worked before I moved the grid to a new form, of the same class. If I remove the UDF (which does work and hasn't changed) the grid works fine.

Could it be that the function isn't visible anymore? Try to suspend the execution while grid is active and call your function in the command window (adjusting for the datasession if necessary). Check the Set("procedure"). Seems that your grid can't evaluate the controlsource because it can't find the function.