This error  is because DNN cant resolve the browser specifically Googlebot Images and we need to tweak DNN core to recognize this browser which will fix this problem.

DotNetNuke.Services.Exceptions.PageLoadException: Value cannot be null.
Parameter name: String ---> System.ArgumentNullException: Value cannot be
null.
Parameter name: String
   at System.Number.StringToNumber(String str, NumberStyles options,
NumberBuffer& number, NumberFormatInfo info, Boolean parseDecimal)
   at System.Number.ParseInt32(String s, NumberStyles style,
NumberFormatInfo info)
   at System.Web.Configuration.HttpCapabilitiesBase.get_MajorVersion()
   at
Solpart.WebControls.SolpartMenu.BrowserSupportsFunctionality(ClientFunctiona
lityEnums
eFunctionality)
   at Solpart.WebControls.SolpartMenu.DownLevelBrowser()
   at Solpart.WebControls.SolpartMenu.getBorderStyle(String type, String
color, Int32 width)
   at Solpart.WebControls.SolpartMenu.getMenuBorderStyle(String
shColor, String hlColor, Int32 width)
   at Solpart.WebControls.SolpartMenu.WriteCSSStyles()
   at Solpart.WebControls.SolpartMenu.Page_PreRender(Object sender,
EventArgs e)
   at System.EventHandler.Invoke(Object sender, EventArgs e)
   at System.Web.UI.Control.OnPreRender(EventArgs e)
   at DotNetNuke.Framework.PageBase.OnPreRender(EventArgs evt) in
C:\dnnRoot\Library\Components\Framework\PageBase.vb:line 549
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Page.ProcessRequestMain(Boolean
includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   --- End of inner exception stack trace --- AdsBot-Google-Mobile
(+http://www.google.com/mobile/adsbot.html) Mozilla (iPhone; U; CPU iPhone
OS 3 0 like Mac OS X) AppleWebKit (KHTML, like
Gecko) Mobile Safari

Caps looks correct ..

I added another .browser file to app_browser folder and trying to catch any
bot from googleAds (made it simple as I don't need version numbers

   <browser id="GoogleAds" parentID="Default">
       <identification>
           <userAgent match="AdsBot" />
       </identification>

       <capabilities>
           <capability name="browser" value="GoogleAds" />
           <capability name="version" value="0" />
           <capability name="majorversion" value="0" />
           <capability name="minorversion" value="0" />
           <capability name="xml" value="true" />
           <capability name="crawler" value="true" />
           <capability name="w3cdomversion" value="1.0" />
           <capability name="tagWriter"
value="System.Web.UI.HtmlTextWriter" />
       </capabilities>
   </browser>

The Null error comes up for this User-Agent:
AdsBot-Google-Mobile (+http://www.google.com/mobile/adsbot.html) Mozilla
(iPhone; U; CPU iPhone OS 3 0 like Mac OS X) AppleWebKit (KHTML, like Gecko)
Mobile Safari