i fixed this in the 0.8.5 version actually (assuming you update the version before you increase the size of the platform) so it can't happen :/
What you can try:
- /dw_reset_harvesters
- /dw_reset_warp_platform
But checking the error, i don't think it'd work... reset_harvesters assume you still have the harvester "valid"
Do you have any save prior to this issue ?