Actually, there were more errors. In the function, you need to declare your
array as that, not as a variant. Also, you cannot redim preserve without
having first dimmed.

Public Function geomsasciiparse() As Variant
Dim logical_layer() As string ' This is not a variant, it is an array of
strings.
Dim logicallayernumber, arraynumber As Integer ' You are just declaring
arraynumber as an integer, logicallayernumber is a variant

Dim objFSO As Object
Set objFSO = CreateObject("Scripting.FileSystemObject")

Dim objGeomsAsciiFile As Object

'Buf array stores words from each line
Dim Buf() As String
Redim logical_layer(0) ' You cannot redim preserve without first dimming
the array (the preserve comes later)

'opening geoms_ascii file as read only from Mentor Design Container
Set objGeomsAsciiFile = objFSO.OpenTextFile(path1 & "\geoms_ascii", 1)

Do While Not objGeomsAsciiFile.AtEndOfStream
strLine = objGeomsAsciiFile.Readline

'look for first instance of _LAYER_DEFNITION in geoms_ascii
If InStr(strLine, "_LAYER_DEFINITION") 0 Then
Buf() = qc_Split(strLine)

'extract logical layer number from ARTWORK_01_LAYER_DEFNITION
logicallayernumber = Mid(Buf(1), 9, 2) ' This is now a string due to use
of mid function

'need to redim logical_layer so it can be assigned to geomsasciiparse later
ReDim Preserve logical_layer(CInt(logicallayernumber)) ' You can't redim
using a string as parameter

'ignore when ARTWORK_LAYER_DEFINITION = 00 in geoms_ascii
If logicallayernumber < "00" Then
For buf_idx = 1 To UBound(Buf)
If InStr(Buf(buf_idx), "SIGNAL") < 0 Or _
InStr(Buf(buf_idx), "POWER") < 0 Then
logical_layer(CInt(logicallayernumber)) = Buf(buf_idx)
Exit For
End If
Next
End If
End If
Loop
geomasasciiparse = logical_layer
objGeomsAsciiFile.Close

End Function