We're having problems sometimes when we try to add an attribute to a LinkItem.Attributes. We have a LinkItemCollection that we're iterating through, for each LinkItem we're adding an attribute like this:

linkItem.Attributes.Remove("class");
			linkItem.Attributes.Add("class", "icon " + @Html.GetFileType(linkItem));

		    if (Html.GetFileType(linkItem).ToString().Equals("pdf"))
		    {
		        linkItem.Attributes.Remove("target");
                linkItem.Attributes.Add("target", "_blank");
		    }

For some reason, the line linkItem.Attributes.Add("target", "_blank") sometimes crashes. This happens very very rarely. I've seen it only a couple of times during a year or so. And it's always the second time we're adding an attribute the exception happens.

Anyone know why this can happen? Or how to prevent this from happening?

See stacktrace below.