Blackskull
Hi everyone, this is my first time here: I don't know if this could solve your problem, but it worked for me. In my case, the operating system (Win 10 pro 21H2) installed on disk2 (500GB SSD Gigabyte GP-ASM2 NVMe). I tried to upgrade to GPT but without success: same error message (all too common). However, I was using the freeware <MiniTool Partition Wizard> to try to switch from MBR to GPT (and I found that it is ONLY possible for the paid version ...) when I found the command "Align All Partition". After some internet research, I found this page <https://superuser.com/questions/225936/what-does-it-mean-to-align-partitions>. Well, even after reading that the command is only for improving the performance of the operating system (... the system really should know the true block size ...) I've try to proceed with this 'feature'. Well, this (IN MY CASE) solved the mbr2gpt /validate error message, so now my OS disk is GPT. This is where I write right now ... good luck.