potentially dangerous Request.Path value was detected from the client - Google Plus Button

I keep getting the following error in a website which has a button linking to our google plus page... I can never recreate the error myself but get this error daily... any ideas?
Error in page http://www.website.co.uk/https:/plus.google.com/123456789/error.aspx?aspxerrorpath=/https:/plus.google.com/123456789
Message
A potentially dangerous Request.Path value was detected from the client (:).
StackTrace
at System.Web.HttpRequest.ValidateInputIfRequiredByConfig() at System.Web.HttpApplication.PipelineStepManager.ValidateHelper(HttpContext context)
Query String
aspxerrorpath=%2fhttps%3a%2fplus.google.com%2f123456789
Thanks in advance :)
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