As hinted by Maciej - you are not extracting the contact person from the database. You need something more like the following (warning - I have not tested in any way)
taAdapter = New OleDbDataAdapter("SELECT [ClientName],[Contact Person] from [Clients] where [Status] = 'Active' ", connection)
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.
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.DisplayMember = "ClientName"
.ValueMember = "Client Person"
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You can then refer to the ValueMember of the selected row to populate your textbox