Mexican Citizen wanting to get business Visa for China

Hello. Im an dual citizen USA/Mexican. Ive been invited to Shanghai by a Chinese company for business and commercial activities for 3 months. They have issued me with an invitation letter for business visa (M) application. I also did study exchange in China 2 years ago and was on an X visa.

I just spoke with my visa agent and he said that I can't apply for business visa because my previous visa was X visa? Is this true?

Can anyone provide some further information on this issue?

Thanks!