I have a user who cannot login to AGOL from ArcGIS Desktop 10.5.1. Under Add Data, the Add Background later function is greyed out. Under the File Menu the Sign in option is greyed out. We have 100's of Desktop installations and only one user is having this problem. He is able to login and access our AGOL organization correctly when using any web browser. ArcGIS Desktop seems to be looking for a non-existent proxy and no proxy is configured in Arc or Windows.
Connection Test results:
Ran ArcGIS Connection Tests -
Proxy Server Test - Failed
Reason Unknown.
Our network does not use a proxy server. I've checked ArcCatalog network settings and Windows network settings to confirm no proxy information is incorrectly entered where there should be none. I have also had him replace Normal.mxt to see if it's an issue with any customizations he is currently using in his mxd files. The behavior is the same in multiple mxds.
Download Speed Test - Failed
Test site unreachable.
Network Latency Test - Passed
Network latency 0 ms. Rating Excellent
Network Route Test - Passed
Network route solved with 1 nodes. Route details :
xyz.xyz.xyz.xyz [<machine name here>]