I'm getting the following exception when trying to add items to a list:

"http://vs-wssdev-001.asplogon.com:8080/legalportal/home/100056/" contains illegal character ':'.

As far as I can see from the code it must be the in this code the exception is thrown:
Dim SpsList As New K2SpsList()

' Set Url for Web Service
SpsList.Url = Server & "_vti_bin/K2SpsList.asmx"

' Set Credentials
Dim SpsUtils As New SourceCode.K2SPUtilities.SPSUtilities
SpsList.Credentials = SpsUtils.GetCredentials(Server)

Why would anyone consider ':' not to be a legal part of a URL?