I had this error when opening notepad and sometimes other software until I reinstalled Windows 2000 yesterday. It's come back after I copied a profile over. Any ideas on how to fix this?
DecodePointer is a function which comes with Windows XP SP2 and is not supported on Windows 2000 (see here). So my guess is that you installed software which is not suited for Windows 2000 and which perhaps overwrote some DLLs with newer improper versions.