Hi,
I'm not sure what you are doing but that is not a reproducible error or bug in mojoPortal as far as I know. If you can reproduce this error on demo.mojoportal.com or provide repeatable steps to produce it I will look into it as a bug.
Only thing I can suggest is try using CKeditor instead of TinyMCE, you can enable it in Administration > Site Settings.
There is a setting in Web.config that determines the max length allowed for query strings
<httpRuntime requestValidationMode="2.0" maxUrlLength="560" maxQueryStringLength="2048" />
but it should be long enough already and I don't know any reason it would give that error in the editor, nor does it happen for me when I paste in the content you posted in html view.
Hope it helps,
Joe