Kindly find this error in below link. You will certainly get an idea about this.
http://www.3cstudios.com/First_Data_LinkPoint_SGS_Error_Codes.aspx#05005
it is saying this about the problem you are having:
SGS-020005: Error (Merchant config file is missing, empty or cannot be read).
Normally you will receive this error when you are trying to use your live account with the staging server. In order to use the staging server you must first setup a separate test account on the following web site:
https://www.linkpoint.com/support/sup_teststore.asp
Also make sure you entered the correct store number. If you are using Yourpay you must enter the 10 digit store number. If you are setting up a shopping cart make sure you enter your store number when prompted for "storename."