Rocket Validator integrates the W3C Validator HTML checker into an automated web crawler.
HTML issues tagged as space not allowed.
An <iframe> element allows to embed an HTML document inside another HTML document, and its src attribute is indicated the source URL of the embedded web page. The query part of that URL contains one or more space characters, which are not allowed, for example:
<iframe src="https://maps.google.it/maps?q=2700 6th Avenue"></iframe>
You should properly escape all space characters as %20 like this:
Still checking your large sites one page at a time?