Forms :: Check Box Drop Down Multi Value Field

Trying to use some code to 'Select All' from a 'Check Box Drop Down' Multi Value Field . The table field size is long integer.

When trying to "Select All" the code returns a RTE 3163 "This field is too small to accept the amount of data you attempted to add. Try inserting or pasting less data".

Private Sub cmdSelectAll_Click()
Dim SelVals, i
ReDim SelVals(0 To lkupAssignedTo.ListCount - 1)
For i = 0 To lkupAssignedTo.ListCount - 1
SelVals(i) = lkupAssignedTo.Column(1, i)
Next i
lkupAssignedTo.Value = SelVals
End Sub

Not my code, but just something I have found and trying to adapt. Tried changing the field sizes but no luck. Maybe something to do with declaring variables perhaps??