So I just tested out your code, and here's your problem:
oItem.SaveAs(sUniqueFileName + ".txt", Microsoft.Office.Interop.Outlook.OlSaveAsType.olTXT);
sUniqueFileName is never set to anything besides null. Not only that, but you didn't specify which folder to save it to.
Also, you don't need to use the OItem_loopVariable.
You could have just written
foreach (oItem in objMAIPFolder.Items)