I just installed version 5.1.0. The exntension install worked fine but now when I install it on my site I receive this error:

Error: UsersOnline is currently unavailable.
DotNetNuke.Services.Exceptions.ModuleLoadException: C:\Windows\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\root\cbdfbc43\822cdeab\App_Web_usersonline.ascx.9f9943af.ttoklclr.0.vb(53): error BC32206: The project currently contains references to more than one version of DotNetNuke, a direct reference to version 5.0.1.189 and an indirect reference (through 'DotNetNuke.Modules.UsersOnline.UsersOnline') to version 5.1.0.501. Change the direct reference to use version 5.1.0.501 (or higher) of DotNetNuke. ---> System.Web.HttpCompileException: C:\Windows\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\root\cbdfbc43\822cdeab\App_Web_usersonline.ascx.9f9943af.ttoklclr.0.vb(53): error BC32206: The project currently contains references to more than one version of DotNetNuke, a direct reference to version 5.0.1.189 and an indirect reference (through 'DotNetNuke.Modules.UsersOnline.UsersOnline') to version 5.1.0.501. Change the direct reference to use version 5.1.0.501 (or higher) of DotNetNuke. at System.Web.Compilation.AssemblyBuilder.Compile() at System.Web.Compilation.BuildProvidersCompiler.PerformBuild() at System.Web.Compilation.BuildManager.CompileWebFile(VirtualPath virtualPath) at System.Web.Compilation.BuildManager.GetVPathBuildResultInternal(VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile) at System.Web.Compilation.BuildManager.GetVPathBuildResultWithNoAssert(HttpContext context, VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile) at System.Web.Compilation.BuildManager.GetVPathBuildResult(HttpContext context, VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile) at System.Web.UI.TemplateControl.LoadControl(VirtualPath virtualPath) at System.Web.UI.TemplateControl.LoadControl(String virtualPath) at DotNetNuke.UI.ControlUtilites.LoadControl[T](TemplateControl containerControl, String ControlSrc) at DotNetNuke.UI.Modules.ModuleHost.LoadModuleControl() --- End of inner exception stack trace ---

I am very new to DNN so any resolution written in simple language will be helpful. Is the issue with the version of DNN I am using. I am not a professional developer so any resolution explanation in simple verbaige will be helpful.