Some names in both Export Kit and other environments are reserved and you cannot use them. We cannot list all reserved names (there are many), but Export Kit has a specific few:

Invalid Names (DO NOT USE):
Untitled-[x].psd
PSD.psd
AI.ai
INDD.indd
[name].PSD
[name].AI
[name].INDD
[0-9][name].psd (start with number)

Use Englis (UTF-8) names for your PSD/AI/INDD files – make sure your first letter is lowercase to avoid errors, along with a lowercase file extension, eg.

Valid Name Examples:
myProject.psd
myproject.psd
my_project.psd
my_PROJECT.psd
my_project_01.psd