I have a project that consists only of a header file and the source file (C). The program compiles, links, and generates the HEX file perfectly. I can then download the HEX file, and it executes perfectly. My problem is that when I create a new project and copy the header file and the source file to the new project, I get ?C_START unresolved external symbol warning, which seems to indicate a problem with STARTUP.A51. But, I'm using the same A51 file as in the previous project. I've also checked the Project Options carefully to make sure they are the same. I'm sure the problem is something obvious, but I'm a newbie, and it's not obvious to me. Any suggestions?