SQL Server 7 and VB6

The table in sql the primary key is an identity field, incremented by 1.

I am creating a data entry app in vb and need to pull the next incremented value from sql in order to save the record.

I have done this in oracle:
declare global variable: Global gvCustid as long
cmdAddnew:
With deCes.rscdInvitee
gvNextCustID = !nextval
End With
txtCustID.Text = gvNextCusID

When I have tried this code I have been receiving the error: field not updatable, bound property.

If this code is eliminated I receive the error from my code. :
updateerror:
MsgBox Err.Description, vbOKOnly + vbCritical, _
"Error"
The description is Errors Occured.

Any advice would be greatly appreciated.

Thank you

Brandy