Previously before .NET this used to be a major issue. DLL Hell refers to the set of problems caused when multiple applications attempt to share a common component like a dynamic link library (DLL) or a Component Object Model (COM) class. In the most typical case one application will install a new version of the shared component that is not backward compatible with the version already on the machine. Although the application that has just been installed works well existing applications that depended on a previous version of the shared component might no longer work. In some cases the cause of the problem is even more subtle. In many cases there is a significant delay before a user discovers that an application has stopped working. As a result it is often difficult to remember when a change was made to the machine that could have affected the application. A user may remember installing something a week ago but there is no obvious correlation between that installation and the behavior they are now seeing. The reason for these issues is that version information about the different components of an application aren't recorded or enforced by the system. Also changes made to the system on behalf of one application will typically affect all applications on the machine.
DLL Hell is nothing but overwriting the dll in the registery. If two application are installed on a single server one installed First and the Second Installed Later and There is a dll with same name with different functionality used in both the applications So in this case Application one works fine all the days until application two Installed on the machine. Once the Application two is installed containing the DLL with the same name as Application one Contains then In this case the application one Fails as the DLL from Application two overwites the DLL of Application one in the Registery. So Application two works fine where as Application one Fails as the DLL is missing.
DDL hell is the problem of registering the DDL .NET remove this problem by assemblies because assemblies has its own meta data thats why it dose'nt require the registration.
