title: Class Library Project File not compiling into .dll or debugging
body: <p>in my solution:</p>
  
  <ul>
  <li>i have a class library project that compiles into a dll.</li>
  <li>i have a web project.</li>
  </ul>
  
  <p>(i have multiple solutions with different web projects but the same class library)</p>
  
  <p>one of the files in the class project (utilities.cs) - all of a sudden won't compile into the .dll</p>
  
  <p>i had made a change to this file, but the change wouldn't show on the website. so i put a breakpoint in the .cs file, and tried running it... breakpoint didn't get hit! eventually i put a breakpoint in the .aspx file that called the function. then i stepped the debugger one line on, so it would step into the .cs file, except i got the error:</p>
  
  <p>"This source file has changed. It no longer matches the version of the file used to build the application being debugged."</p>
  
  <p>so the code in utilities.cs is not being updated into the dll. which is weird, because code in my other .cs files IS being updated (i tried changing a few lines) and IS able to catch the debug.</p>
  
  <p>any ideas how to fix this? or even what the cause of the problem is??</p>