Installation of Outlook plugin

0

Hello!
I've come accross a problem with installation of Outlook plugin (the full version of Outlook, the application, not the O365 lite one). Tried to do this in Internet Explorer, run as admin, with no luck. There is an error message saying the certificate used to sign the manifest or its' localisation is are not trusted. At the bottom of the error message there is a sentence saying the zone is incorrect: MyComputer. However there is no choice where to place the certificate or where to look for it. I've installed the plugin on several other machines with no trouble... The error message below (in Polish, as this is the language of my installation). What could be the problem? How can it be solved?

Error message:

Nazwa: WEBCON BPS for Microsoft Outlook AddIn
Od: http://webcon.artlocum.pl/addins/outlook/WebCon.WorkFlow.Outlook.vsto

************** Tekst wyjątku **************
System.Security.SecurityException: Dostosowane funkcje zawarte w tej aplikacji nie będą działać, ponieważ certyfikat użyty do podpisania manifestu wdrożenia dostosowania WEBCON BPS for Microsoft Outlook AddIn lub jego lokalizacja nie są zaufane. Aby uzyskać dalszą pomoc, skontaktuj się z administratorem.
w Microsoft.VisualStudio.Tools.Applications.Deployment.ClickOnceAddInTrustEvaluator.VerifyTrustPromptKeyInternal(ClickOnceTrustPromptKeyValue promptKeyValue, DeploymentSignatureInformation signatureInformation, String productName)
w Microsoft.VisualStudio.Tools.Applications.Deployment.ClickOnceAddInTrustEvaluator.VerifyTrustUsingPromptKey(Uri manifest, DeploymentSignatureInformation signatureInformation, String productName)
w Microsoft.VisualStudio.Tools.Applications.Deployment.ClickOnceAddInDeploymentManager.VerifySecurity(ActivationContext context, Uri manifest, AddInInstallationStatus installState)
w Microsoft.VisualStudio.Tools.Applications.Deployment.ClickOnceAddInDeploymentManager.InstallAddIn()
Niewłaściwa strefa zestawu to:
MyComputer