It sounds to me as if either of the following two things has occurred:
1) There was a defect in the original construction resulting the damp problem. Perhaps the damp course was not done properly or subsoil drainage was not provided.
2) Something has been done on the common property subsequent to construction that has caused the problem. Perhaps the soil level has been built up higher than the original waterproofing.
Either way it seems the owners corporation should take the advice of a building engineer to identify the cause and to recommend the best way to fix it. Then it is an owners corporation expense. An appropriate thing to spend money from the sinking fund on or to have a special levy or to take a loan.