Simply stated, most banks see the neighborhood as a high risk investment if the current owners are not paying their HOA dues or if the majority of the units are rented and not owner occupied. They do not want to loan buyers the money to buy a home in these areas. The presumption is that it's very likely the units not being cared for and maintained because of either financial difficulties or because they're tenants who do not (normally) have the same vested interest in the property. FHA has established an "approval" system for HOA and condo communities. If a community does not meet their approval, they will not back the loan. If FHA won't back it, most other banks follow suit and won't either.
Jody and Tony hit it on the head. I am assuming you are looking at TH that has comments of cash only for sale. You may need to seek some alternative financing if this is the case. call me if you need any assistance.
The problem would be that the community has probably lost it's FHA certification. It would no longer be eligible for FHA backed loans, but should still be able to qualify for conventional financing with some lenders.