Is it possible to copy files to PC when in download mode? My LG E975 doesn't boot anymore after I tried to install CWM (6.0.4.5) with the help of ROM Manager (Method 1A from these instructions). I get stucked at the reboot into the stock recovery part and now the device doesn't work anymore. I get the message

Secure booting Error! Cause: boot certification verifiy


The available options are hard reset and the download mode. Recovery mode (in FastBoot mode press 2x Volume Down and than Power) doesn't work because the device doesn't get in the fast boot mode (Volume Up + Power). Safe mode (Power + Menu button) also doesn't work. Because I wan't to access the files (apps, data, ...) on the phone I thought if there is a possibility to copy the files if I'm in download mode? Or is there another way to access the data?

PS: Has this problem happened because the bootloader was not unlocked?
No, download mode doesn't provide you with access to the phone's files, and yes, the error message you see looks very much like it's telling you you're trying to boot an unsigned ROM from a locked bootloader.