Problem with outdated .dll

Question

I have a project that needs a .dll from another class library project.  I updated the dll today and my project will NOT use the new version.  It's crazy.  I completely deleted the dll with yesterday's date from the file system.  But, when I recompile in VStudio the dll that gets brought into the project is the old file with yesterday's date.  I have no idea where the heck it's coming from.  I thought it would bring in the dll with today's date (which is the latest release).  Any idea how this could happen?  And, how to correct?  I'm going nuts with this!