From my team (too technical for me - hopefully it will be useful to you):
""Server name, instance name and port is pulled automatically for them. They will have to follow below steps.
1, Insert CRM URL to trusted sites in IE browser.
2. Set the security to low in trusted site zone in IE.
3. Close the IE and open again and start installing the plugin
If they still have issues, they have to use the servername as customersite.crm.com and instance name as specified in the URL. Hope this helps""
Also, if they use https in their URL, they will need to make sure
1. port is set to 443
2. https check box is 'checked'""
Does that help Katrina?