nested aggregation

[JoseGarcia]

Hi,
Expression below is giving me nested aggregation error.

Could anyone assist?
thanks 

=avg(sum([EightD.Date_Creation])- sum([EightD.D1_KPIDate])) 

[Channa]

why you are using average there remove that avg

[JoseGarcia]

If no selection made, I need average time.

[MarcoWedel]

You need to elaborate on your actual requirement.