Do following

1. Check if system account has permission on c Drive , if not add then run scan.

2. Try updating windows agent by downloading the same from MS site.

We had similar issue lately on our win7 machines. The following KB resolved this issue for us. 

Note: Installing this update requires system restart.

https://support.microsoft.com/en-us/kb/3112343 

can you please help me windwos agent for windwos 8 , windows 7 had I have not able to find the update for windwos 8 and 8.1

The Windows Update Agent Engine has been updated about 6 times in the last year alone,  the Radia Patch agent has a built in ability to update the Windows Update Agent engine but I think Microsoft may have changed the way they publish the WUA Engine updates so the latest version the Radia Patch agent can push is very outdated.  

See Also:  https://support.microsoft.com/en-us/kb/3138615

AND https://support.microsoft.com/en-us/kb/3138612

NOTE:

Accelerate can publish many non-security patches such as this for acquisition using the non-security patch option if it is available to you in your installation/version of Radia.  You can also acquire it as a custom patch by requesting it from the Radia Support team.

Here is where the Radia Support Team publishes their list of non-security patches if you have that option available in your Radia version/installation.

http://patchcontent.accelerite.com/Radia/patch_management/data/info/bulletins/non_security_bulletins.html

PS.  I have already requested these updates be made acquirable as a non-security patch from Radia Support so the turn around time on your request should be really quick.

Some of our Radia support customers had a problem in January so I created a custom bulletin and sent out an alert. I wasn't sure at the time how Patch manager would handle the update once the problem was already present.

Sent: Wednesday, January 27, 2016 6:57 PM

I created a custom bulletin to update Windows Update via Radia Patch manager and uploaded the export deck to ftp/17403/MS-KB3112343.ZIP. The export is for Windows 7 (32/64) only. Import the deck and assign in policy to test the functionality.  Once the Windows Update agent is updated a reboot will be required in order for the Windows Update to complete the update to 7.6.7601.19077.  I am not sure how Patch Manager will handle this update when the “WUA Scan failed with Not enough storage is available to complete this operation “ is already present so please test and let me know if this resolves the problem or not. Alternately, you can publish and distribute the Windows Update agent via Software Manager. Let me know if you have any questions or issues.

https://support.microsoft.com/en-us/kb/3112343

Please open up a support case with Acccelerite, and someone from the team will assist you further with your request.