This is some information that I would like to share with our customers that could be of help. This is situation is not common, however, we did see if for one of our customers and the fix that was found can potentially help others.
After going through the basic agent troubleshooting where an agent would not install, it was found to be a bit of an environmental issue. It was found that a Windows 2008 R2 server had a Windows environment variable set for HTTP_PROXY which pointed to the customers proxy service. Curl.exe uses this same environmental variable, which then the Kaseya agent will use. Once the environmental variable on the server was changed to something other than HTTP_PROXY and changed the related services to run as a local system, the agent installation issue was resolved.
Again, this is not something that is common - however, I thought it would be good information to pass along in the event that other customers may be using this same variable in their environment and are having agent installation issues.