I had a small problem when I changed the pxemode in the admin setting from previously ipxe to pxelinux (because I had some Dell servers that did not boot with ipxe).
I had permanent active tasks for some machines and had the pxe-files "mac.ipxe" for them.
Then I switch to pxelinux.
If I then go to "Computers" and select one of those machines and try to open the "Boot menu", the gui tries to find the pxe-config-file for the machines but now without the extension ".ipxe".
This file didn't exist and so it shows "Could Not Read File" (FileOps.cs )
To fix I had to recreate the permanent tasks.