A command button fires the following code

Range("AV10").Select
Selection.AutoFill Destination:=Range("AV10:AV7800"), Type:=xlFillDefault
Range("AV10:AV7800").Select

When AV2967 is reached the following formula changes from

{=IF(SUM(--('A Use'!A$1:A$10000&'A Use'!C$1:C$10000=B2962&"G house")),"G
house","")}

to:

{=#VALUE!}

If I manually fill down the formula past where it changes to {=#VALUE!} the
formula does not revert to {=#VALUE!}

Does anyone know why the formula suddenly should change