The local authority spent pound;50,000 upgrading the ventilation system and ripping up carpets amid fears that adhesives were causing breathing difficulties. But it was in vain.
Now supernatural solutions are being used to try to lift the curse on the Meadows special school, in Sandwell, near Birmingham.
An exorcist has performed a ritual on the pound;5 million school after other attempts to find the cause of the illnesses - which have seen the head and six teachers complain of allergic reactions - failed.
In the past two years, seven staff have been temporarily forced to leave the school, which was officially opened by Margaret Hodge, former children's minister, in 2004.
Ian Jones, Sandwell council's education spokesman, revealed that the exorcist was among a number of people who wrote to the authority offering to solve the mystery.
He said: "We were contacted by an exorcist who apparently did his stuff from afar, using some sort of remote control technique and looking at a map. We did not commission him.
"We have also had letters from other people including an extra-magnetic field expert. All the letters have been passed to the education department which will assess if they can be of any use."
The Meadows, which has 143 pupils aged 11 to 19 with profound learning difficulties, opened in October 2004. Angela Duncan, headteacher, became ill soon after and doctors said she was allergic to materials used in its building.
She has since been seconded to other duties because she cannot return to the building, which was erected on the site of a primary school.
The six other members of staff complained of similar respiratory problems.
Independent experts, including the health and safety executive, have since carried out separate investigations. The school has declined to comment.