Could not load file or assembly ‘itextsharp, Version=5.5.0.0, Culture=neutral, PublicKeyToken=8354ae6d2174ddca’ or one of its dependencies

I have used itextsharp library to generate pdf in my asp.net web application. It was working fine untill today when suddenly my laptop on which the application was running in the debug mode went off. When I switched on my laptop again and tried to run the application I satrted getting this error: