Downgrade CM13 to stock failed

Hi,

i tried to downgrade CM 13 to the Stock Android 5.0.2 and relock it (I know that Motorla has the unlock indicator, but this doesn't matter here).

So I tried the following steps as descripted in a lot of posts, but every command failed:

Code:

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fastboot oem lock begin //success
fastboot flash partition gpt.bin // Preflash validation failed ->version downgraded for primary gpt
fastboot flash motoboot motoboot.img //  Preflash validation for tz -> version downgraded for tz
fastboot flash boot boot.img //  Preflash validation failed -> version downgraded for boot

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So how can I solve the problem? I think it has something to do with downgrading :P