The breakpoint will not currently be hit. Error

Question

Hello All,

             I am working with windows application C# , i have a solution with 3 projects , projects 1 and 2 are referenced in the 3rd. i had to make a small change(consider bool a = true to false) in 1st project. after this i placed a break point in 1st solution where i made the changes. but at break point i get a strange message like

"The breakpoint will not currently be hit.  The source code is different then the original version".

and after that when i build every thing builds properly newer dlls are created and when i run the project 3, the below things happen

1. does not go to the break point.

2. The changes made in the code does not get reflect in new build

Any ideas..

Thanks

Vishwas