Condo's are generally a little more difficult than any single family detached home because they do have to go through another step or level of Underwriting. The actual Homeowners Association or HOA has to be looked at. The by laws, covenants, investor ownership are all reviewed to make sure it meets Conventional loan guidelines.
Is there a particular condo complex that you are inquiring about? If so, i would be happy to look into it for you to see if it would be eligible for conventional financing. If it's not, my company Guaranteed Rate, Inc has multiple portfolio loan options if you are looking to buy a condo that doesn't fit inside the box described above.