It's always a great idea to check the validator at w3 can be frustating getting your page to validate, but at least you will eliminate any spidering issue
A crawler/robot/spider does no more than simply request a resource; whether or not such requests succeed or fail are wholly independent of the data contained within said resource.
Parsing of such data is performed by the indexing engine; and, as are browsers, such engines are very good at distinguishing between code and contextual data. As it is the latter alone that is indexed, whether or not the former is compliant with any standard is irrelevant.
If a text only browser, such as LYNX, can properly display the textual content of a page, an SE's indexing engine will have no problem with it.
Thanks Tim for the very useful suggestions. Tried the sitereportcard.com and found it very useful. I just don't know how to make adjustments on the Load Time Check where I failed miserably at 1/10. Can you help me please?