Split Database would not recognise .Index

[Joseph Yeo]

I have the following codes which works perfectly:
Dim Db As Database
Dim Rs As Recordset
On Error GoTo ErrorControl
Set Db = CurrentDb
Set Rs = Db.OpenRecordset("Clients")
Rs.Index = "PersonID"
Rs.Seek "=", CLng(PersonID)
However, after splitting the database, I get an error message on this line:

Rs.Index = "PersonID"
"Operation is not supported for this type of object"

Any ideas why? Please help.