0x800706ba (most frequent error)

In this case, wmic may also report an empty output. For more details, about this symptom, see Discovery: How to test the WMI connection with wmic?
The error may in include "The RPC server is unavailable"
Root Cause: the required ports documented in the section "WMI" in this page are not open

0x80070422

The error may also include "The service cannot be started, either because it is disabled or because it has no enabled devices associated with it."
Root Cause: the WMI service on the target host is stopped

0x800706b5

The error may also include "The interface is unknown"
Root cause 1: NT AUTHORITY\SERVICE is not in Administrators Group

Solution: Re-register WMI components and add NT AUTHORITY\SERVICE  to Administrators Group.

Root cause 2: some WMI components are corrupted

0x80041004

In this case, wmic may also report "Failed to access Win32_NetworkAdapter : Failed to retrieve batch of results : 0x80041004 : Provider Failure"
see the article below:
Discovery: Failed to access Win32_NetworkAdapter : Failed to retrieve batch of results : 0x80041004 : Provider Failure.
 

0x80070005
            The error may also include "Access is denied"

Root cause 1:  Incorrect domain and/or user and/or password.

Root cause 2: UAC is enabled. It has to be disabled in certain cases (see "UAC" in this page). See this article.

Root cause 3: The credential does not have the required permissions as documented here. See the section "Granting permissions".

0x800706be (in proxy debug logs)

The error may also include "The remote procedure call failed"
This page suggest some checkpoints/causes/solutions for this error.
extract: “… occurs when a RPC query times out”
See also this page:
extract: “… can be caused by a number of different factors including software incompatibility or corrupt files”

0x800706bf 

The error may also include "The remote procedure call failed and did not execute"
In this case, the scan of Windows 2012 server ends with NoAccess, and a credential test may fails with "Remote Access via Windows Credential Proxy xxxxxxx failed".  
This page suggest some checkpoints/causes/solutions for this error.
extract:
“… result of cluttered Windows registry or faulty entries of non-existent programs which are usually due to improper software uninstalls”
“… incorrect user input, missing files that were accidentally deleted from the registry and cause system malfunctions.”

0x80041003

The error may also include "Access denied"
Root cause: the scanned device is not in the TrustedHosts list of WinRM (Windows Remote Management)
Solution: execute the command below on the proxy
winrm s winrm/config/client @{TrustedHosts="*"}

0x80070721
            Testing with wbemtest results in "A Security package specific error occurred"
            Root cause 1:  Time difference between Outpost and scanned device

For a detailed step by step guide on how to troubleshoot Windows WMI discovery failures please see following video