If you have removed the dust and the vents are unobstructed, but the projector still indicates that it is overheating, then the thermal sensor may be faulty and it will need to be replaced.
You can try measuring the internal temperature with a thermometer - this will help to confirm if it is overheating or not. If the temperature is really not too high, then this confirms that the thermal sensor is faulty.
Please reply here rather than starting a new question.
You will need to contact Epson and request a replacement sensor from them. They typically cost under $20.
Just one other thing to check as well - make sure the fans are working; if they are not, you will also get overheating error.