Dependency Walker is a free utility that scans any 32-bit or 64-bit Windows module (exe, dll, ocx, sys, etc.) and builds a hierarchical tree diagram of all dependent modules.
You can download this free utility from http://www.dependencywalker.com/
And a very handy FAQ about this tool is available in http://www.dependencywalker.com/faq.html.
You might have faced similar issue noted below while dealing with applications.
Then there should be a dependency for the DLL. To trouble shoot this issue you can use DEPENDANCY WALKER to see if any other files/DLLs are dependant.