Symptoms

When generating an HTML based documentation format, an error occurs saying that it is not possible to create a specific file.


Solutions

HelpNDoc uses the each topic's unique help Id as it's file name. However, some file names (such as CON, NUL, COM1, LPT1...) are not valid file names, and Microsoft Windows will not allow the file to be created.


From Microsoft's documentation:

Do not use the following reserved names for the name of a file: CON, PRN, AUX, NUL, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, and LPT9. Also avoid these names followed immediately by an extension; for example, NUL.txt is not recommended.


The only solution is to change the problematic topic's Help Id and use a value which will be accepted as a valid file name by Microsoft Windows.