My guess is that the Linux kernel reports the same number of heads (255) to sfdisk as it did to ms-sys. Trying to write 255 again is probably not going to help. Reformatting the file system from scratch and restoring a backup might be the simplest solution. Unless you have more questions within the next week I will close this support request.
It is fully possible to do a legacy boot also with a GPT partition table. However, most new machines have UEFI boot and ms-sys is not useful for UEFI boot systems. For UEFI boot a GPT partition table is required, but a GPT partition table does not require UEFI boot. I am not aware of any other way than lilo to find out the number of heads to give to ms-sys. However, there is another tool called testdisk: https://www.cgsecurity.org/wiki/TestDisk . I have used it a few times to restore erased partitions...
The --partition switch does not in any way alter the partition table, only the file system of the given partition (in this case sda1). This can be done on FAT or NTFS file systems. Usually ms-sys is able to get everything right automagically except for the number of heads. So ms-sys has the switch -H where you manually can set the expected number of heads of the disk. Did you by any chance boot your Linux system with lilo? If so, you can use "lilo -T geom" to see the number of heads of your drive...
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