Generally, it is not a good idea to run simultaneous builds on the same machine, and we do not recommend it. However, if you want to attempt a simultaneous build, you can do so at your own risk. As a minimum, take the following precaution: set the TMP environment variable to a different directory for each MS-DOS or OS/2 screen running the Help compiler. Otherwise, temporary filenames that the Help compiler creates during the build may collide, producing very bad results.