Are you on a Windows server or Linux?
Shared or VPS/Dedi.
If shared, your node by be overloaded.
That error appears to be a Windows Server one... and normally is a problem on your server end (your host) with either being mis-configured or overloaded.
It could also be a router/gateway issue with your host, your ISP or even your computer.
Try performing the actions from another computer (and if possible from another location) and see if it still happens.
Suggestion... unless absolutely needing IIS for some reason - dump it and get on a host with a REAL operating system.
Check your firewalls then. That is typically a windows looking error.
Have you checked your logs on the VPS? If running CSF, try disabling that and see if it works. It could also be due to your PHP timing out while waiting for the process to finish.