Realty Times has an article which explains the Fannie Mae changes to rules for loans to investors purchasing a condo. Fannie Mae tries to control the percentage of units within condominium communities that are not owner occupied by restricting loans if the percentage of investor owned properties is too high.
If you are considering purchasing an investment property, you should begin by talking with a lender. Downpayment requirements and other criteria are different than criteria for homes that will be occupied by the owner. Also, let the lender know if you are planning on purchasing a condo as an investment property. The lender should be able to explain to you any special rules for condo loans.