Sometimes the crash to desktop (CTD) is accompanied by Windows informing you that OFP has caused an invalid page fault or fatal exception error.
OFP may require a lot of memory when saving or completing a mission. Increase your Windows swap file size to at least 400MB. If the problem continues, try increasing the maximum swap file size to 1000MB.
If you're running original version 1.75 of OFP: Resistance, you should upgrade to the latest version available, as significant memory utilization reduction was introduced as of version 1.85.
If that doesn't help and you're specifically getting the CTDs when a campaign mission completes, check out this FAQ item.