If a person uses the wrong form of your or you're, would that be considered a spelling or grammatical error? I can really see it swinging both ways...
A sentence with the incorrect use of the word is technically grammatically incorrect, but the root cause could be simple spelling error. If a person speaks a sentence with an incorrect use of the word in question, it seems grammatically correct. When you look at the reader's script, it is then determined to be a spelling error.
When shown in writing, should the error be marked as a spelling or grammatical error?