WOTC - Errors in calculating CHAS subsidy

I asked this question in the Wisdom of the Crowd:

What are your views about the errors in the CHAS subsidies?

Here are the responses: (52 Votes)

69 % - We are now seeing many errors due to the outsourcing and slack supervision.
27 % - This kind of mistake is likely to occur from time to time due to the difficulty of applying complicated formula.
2 % - It is just a once off mistake. 
2 % - The mistake could be due to wrong data on income and type of housing.

See the pie chart at: 
http://www.wisdomofthecrowd.sg/chart.aspx?ID=1188