Special assessments are typically seen when the condominium association's short term expenses exceed their cash on hand. In the case of Bergenwood Commons, the buildings needed exterior repairs (roofing and siding, I believe) , and the association did not have sufficient money to pay. The result was a one-time charge of ~$20k per homeowner. (that is a ballpark figure only). I believe the homeowners had the option to pay the assessment in monthly installments over a period of 15 years. (the above info may not be entirely accurate since I am not a homeowner in that complex)
I am not 100% on the motivation behind the lawsuit. It seems reasonable, though, that the homeowners may have sought a change in the association board after the assessment was levied. (but that is mostly speculation on my part).
What I can say for sure is that those problems are very likely to disqualify the Bergenwood Commons complex from competitive (conforming or FHA) mortgages.