A family of Microsoft relational database management systems designed for ease of use.
Hmm, I've imported so large files so not sure size is an issue. If these files you are trying to import are from and external source they may contain *hidden* characters that are causing the problem. So may not *see* what the problem is.
What I do when an import fails and it's from an external source is open in Excel and save it as an XLS. This 99% of the time either eliminates the *hidden* characters or exposes them which I can then remove. I would give that a try and see if that works.