Caeruleus, that is the normal invitation letter suitable for (most) private visits for family and friends.
What Sandy92 describes, "duly authorized invitation letter", is different. It is usually associated with business visits, but in Sandy's case the requirement seems to be extended for tourist visa as well.
"I'm NOT applying for a business visa but the embassy wants me to have a duly authorized invitation letter anyway; an Invitation Letter it's not enough even if it is from a company"
Could the problem be, that you are applying for tourist visa with company invitation?
Perhaps the the fact that it's a company invitation, triggers the requirement for duly authorized invitation letter, regardless of the type of visa.
Newest form of foreigner owned business entity in China is FIPE, or Foreign Invested Partnership Enterprise.
This model has no minimum capital investment or corporate taxes, so it is very well suited for startups.
However, when I have discussed this with Kunming business consultants, they have said that although the company itself can be started with minimal investment, the foreigner working in such company will have to provide bank deposit or other proof of means to live in China.
In other business models, the capital investment serves for this purpose.