Constant Contact API Error

Ive found the issue. My loop is incorrect, the last cycle of my loop is insert a %0A, how can i make it so that on the last leg of the loop %0A is not inserted?

Without looking at your encoded URL to see the exact issue I believe the problem is in your population loop:
 
While dr.Read()
If dr(1).ToString <> "" Then
data.Append(HttpUtility.UrlEncode((dr(0).ToString() & ", "), Encoding.UTF8))
data.Append(HttpUtility.UrlEncode(dr(1).ToString(), Encoding.UTF8))
data.Append(HttpUtility.UrlEncode(vbLf, Encoding.UTF8))
End If
End While
 
You put a %0A at the end of every entry up until the addition of the data.Append("&lists=") command. This results in an extra %0A before the &lists= in the encode URL. Notice this example of a working string and you should see what I'm talking about:
 
activityType=SV_ADD
&data=Email+Address%2CFirst+Name%2CLast+Name%0A
wstest3%40example.com%2C+Fred%2C+Test%0A
wstest4%40example.com%2C+Joan%2C+Test%0A
wstest5%40example.com%2C+Ann%2C+Test <--- Note there is no %0A here
&lists=http%3A%2F%2Fapi.constantcontact.com%2Fws%2Fcustomers%2Fjoesflowers%2Flists%2F2
&lists=http%3A%2F%2Fapi.constantcontact.com%2Fws%2Fcustomers%2Fjoesflowers%2Flists%2F5

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