Try asking if the customer can reach the following sites in an internet browser window:


If this works, the error is likely being caused by a firewall blocking the designer. Finding the anti-virus software affecting the designer and turning it off or whitelisting Spark should solve the issue.

Alternatively, reinstalling the Admin only can often clear up the issue.

Alternatively, we tried updating her IIS setting, but this solution does not always solve the problem. 

- under sites -

"HttpRootUrl" and added value as

Known Causes:

Web Root antivirus software from a component called Web Shield. Once we turned this off the connection worked fine.