Visa on arrival for businessmen

I was not approved visa on arrival in Shanghai, although I fulfilled the first two of the stated requirements: "They are invited at the last moment by a Chinese host to come to China for a trade fair" and "They are invited to come to China to submit a tender or to sign a formal economic or trade contract".

The invitation was OK for my local application centre in Sweden, but it was too late to get a regular one. Thus I trusted this information and went away - but went sent back with first available flight.

Any idea what was wrong?