IDA cannot change the segment start address because this segment with the
new start address would overlap another adjacent segment. For example,
the following situation:
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seg_a starts at 0x0000 ends at 0x1000 seg_b starts at 0x1000 ends at 0x2000 seg_c starts at 0x2000 ends at 0x3000If you ask to change seg_c so that it starts at 0x500, you'll see this error message, because the new seg_c would overlap seg_b.
Please note that the end address never belongs to the segment in IDA.