Hi Kam,
This error occurs because there was an error during the gene mapping step.
I would need to have your input file in order to further troubleshoot, so please send it to our email address.
In addition, I investigated a similar issue in the past, and this might be something you can try:
https://groups.google.com/g/fuma-gwas-users/c/UqOiHVJ-RCU/m/A2uMhJVbAQAJ
Best,
Tanya