Painting - Peeling wall paint

My house was build in the 50's and the previous owner didn't have a shower or a ceiling fan. I have added both when I moved in 9 years ago. The problem I'm having is, I can't keep paint on the walls. I've scraped, sanded, primed and painted a few times but it just keeps peeling off. The guy at the local paint store said that some older houses, with plaster walls, loose the ability to hold the paint on the walls. He told me I should probably replace or drywall over the existing walls. I'm not liking that answer, anyone ever had this problem and found a better solution? :wall:

I'm not a pro painter, but that sounds rather ridiculous. What kind of primer & paint have you used? Oil or latex and what brand of paint?

That does sound ridiculous. Was this advice from a paint store or a big box?

1. Are you sure its plaster? My first house was built in the 50's and it had sheetrock, not plaster.
2. Does the paint peel all the way to the palster/drywall or is the primer intact?
3. Do you have an exhaust fan? Do you use it? Does it exhaust to the outside or just to the attic?
4. What type and brand of paint are you using?
5. After sanding, are you removing all the dust?
6. What condition is the plaster/drywall under the peeling paint?