VSTO addin Unknown Publisher error

Hi,

I am currently creating a VSTO addin for powerpoint. I am using Visual Studio 2008 development framework for the same.
When I try to install the VSTO on my machine, it gives me 'unknown publisher' error.
To handle this issue I tried out the following:
1. Signing the manifest as well as the vsto with clickonce tool which is inbuilt in powerpoint addin project of Visual Studio 2008 with authentic certificate
2. Signing the dlls as well with the same.
But despite this, I get an 'Unknown Publisher' pop up while installing VSTO.
Then I installed the certificate on my machine and the 'Unknown Publisher' error never occured.
But on other machines where certificate is not installed it gives the same error.
So I tried another approach wherein I sign the vsto and dlls and manifest explicitly by Mage.exe.
However, it gave the same error while installing on other machine. Please note that the certificate that I use for signing is verified from certificate authority

Please could anyone tell me how to handle this issue.

Thanks