Regarding file association in ICS I have a Micromax Supercanvas 2 phone. 

I installed ES File Explorer from Play Store. I was browsing through various directories and files. When trying to open server logs, events, and other similar files, I was asked to open the file from a list of applications (e.g HTML viewer, ES file viewer, etc.) I selected Android HTML Viewer (as default). No file content is shown. Instead, an error is shown that file does not exist on path.

I tried going through all android apps and removing the cache and defaults. It did not remove the association. It still opens files in HTML Viewer. 

Is there any way to remove the association, so that I can select which app to use to open the file?

Thanks in advance for any help.
From my experience, I think ES's default app associations are separate from the operating system's. To clear ES's file associations (assuming you are using the latest version), from ES File explorer go to Settings > Cleanup setting > Clear defaults.

The next time you try to open a  file ES File explorer should now ask which application you want to open the file with.