You are only passing in one file. Try passing in an array of files and loop through the array. Or, since it looks like its semicolon delimiting the list of files selected, try to just split the list...
For Each s As String in sFilePath.Split(";"c)
lobj_cdomsg.AddAttachemt(s)
Next
I have no idea how to run a vb 6 app anymore, but if this helps, please mark it so.