Question: I applied for a reference no. on the Iranian MFA website for a VOA, which was recommended by my embassy. After 3 days I got the following mail:

Dear Mr./ Mrs.  
Having considered your visa request No. 20000........ , we hereby inform you that the submitted information is incomplete. Hence, if you are still interested your request to be reconsidered, you are advised to provide us with appropriate information as well as a copy of your passport via the web site.
Best regards.
M.F.A / Passport and Visa Office.

I am quite sure I filled out everything properly (otherwise you can´t send the form anyway), I have no idea what they want. I filled it out again. Do you have any experience?

Answer: It is better to apply through an Iran based travel agent because they are more familiar with the rules. Some details about Iran visa are available below:
1. Fill in the visa form on http://www.uppersia.com/Iran-Visa-Box/iran-visa-authorization-reference-number-invitation-application-form.html, it takes about 10-15 working days to get your reference number and two working days to collect your visa at the embassy by direct referral or one working week by posting the docs to the embassy. You can pay the visa fee in cash in Iran.

2. Fly to Iran and get a 14-day on arrival visa at the airport. This kind of visa is issued for 98 nationalities excluding USA, England, Canada, Colombia, Pakistan, Afghanistan, Iraq, Jordan, Bangladesh, and Somalia. If your nationality is among the countries authorized to get it, you can easily collect you visa against offering your passport, a passport-size photo and about $50 to the staff at the airport. There is no need to fill in any form beforehand.

3. Refer to the Iranian embassy in your country and ask for a visa to be issued for you. Usually this way takes longer time about 30 days.