There is no check associated with overdue servers, but they should be addressed quickly. Overdue server checks fail mostly because of loss of internet for the computer being monitored.
To Resolve: Edit
1. Make sure the computer being monitored can connect to the internet. If it cannot, follow the steps in "One Computer Cannot Access the Internet".
2. If they can and GFI is running and is "Active", then try this fix: (Note: You may have an error message about "Not Communicating" of some sort)
a. Apply this MS Fixit and restart the agent: http://support.microsoft.com/kb/2801679
b. To restart the agent, run "services.msc" and restart the "Advanced Monitoring Agent" Service.
3. If the agent is in "Maintenance" mode, then you simply need to switch it to "Active".
For "Upload Error" in the Agent's GUI: Edit
1. Make sure there is a secondary DNS on the NIC. Run - ncpa.cpl - Right click on the NIC - Local Area Connection - Properties - IPv4 Settings - Set a static secondary, typically 220.127.116.11 or 18.104.22.168 (Google's Open DNS Server's)
2. You will also see that some webpage's not resolving but you can ping them by IP. This is a tall tale sign of a DNS issue.