During the most recent upgrade I was upgrading from 10.0.1.0 build 44 to 10.2.0.0 build 189 when I received the error. I have received this error with previous firmware versions, but I was lucky and didn't run into an error this time upgrading from 9.13 to 10.0.1. After I attempted to upload the config, I waited a few minutes and tried again with no success. I went into configure>system and turned off NTP and made sure that I synced the time with my computer and I still ran into the issue. I was uploading the new img file from a share drive but have since moved it to my computer for speed and troubleshooting sake. It was only after several attempts that the file uploaded successfully with no errors and I could upgrade.