this is due to attempting to run an MP turn with v1.0.1 when your opponent is using v1.0.2."Size does not match" lists numbers for state: 762884 & Call: 697348
Updating to v1.0.2 should solve the issue.
Normally the server should issue a warning, but the version number had not been updated in the server. This has now been rectified, which will prevent people from inadvertently logging on to MP with v1.0.1. Sorry for the inconvenience.