Some time ago I was thinking of deleting a .dll file but did NOT go ahead with it after reading the following caution notice: You are attempting to open a file of type'Application Extension' (.dll) These files are used by the operating system and by various programs. Editing and modifying them could damage your system. If you still want to open the file, click Open with, otherwise, click cancel.
Ever since then this notice pops up when I start my computer. How can I stop it popping up and staying there until I press 'cancel'?
It sounds like you have an incomplete removal of your old Epson printer installation and now cannot uninstall the remnants. The fix that I have used for this problem in the past (usually with success, I hasten to add) is to completely reinstall the application (or in your case your old printer), reboot, and then uninstall using the Windows uninstaller. This replaces missing files and then removes the lot, hopefully! Otherwise, as others have said, it's probably a trek into the dank areas of the registry or simply disabling the program from running (not really the best of answers, in my book, though as a workaround it'll do).