You may have to modify the Excel Macro for Voucher upload, in case you are using a load balancer in front of your Web servers.
The reason for this is that the technology used in this macro (xml link) does not behave the same as a direct connection to the PIA.
Search for this code in the macro:
xHTTP.Open "POST", Sheets(1).Range("K2") & "/Excel_Voucher_Import", False
And replace it by:
xHTTP.Open "POST", Sheets(1).Range("K2"), False
Edit cell K2 and set it to :