Attachment folders are named according to the project key. Under Windows, some folder names are illegal, preventing attachment folders being created.

The following will all cause errors and cannot be created:
PRN, AUX, CLOCK$, NUL, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9, CON, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, and LPT9