Hi, It seems that the serialization library shipped with boost 1.42 changed the way class versions are handled. The version_type which used to be an unsigned int is now an uint_least16_t, although I found no mention of that in the release notes. The problem is that we are using a date-based versioning scheme for our classes (for example a developer making a change in some class on 2010-02-22 would increment the class version to 20100222). This scheme worked great for a couple of years, and helped us fix our backward compatibility bugs after the fact. Unfortunately, these big version numbers do not fit in 16-bit integers. As a consequence, the version string output in xml archives with the latest boost-serialization for this example would be 46206 instead of 20100222, breaking our reloading code. May I ask why this change was made? Would it be possible to revert it for the next boost release? If not, anyone has suggestions how we could fix our code while maintaining backward compatibility ? (we have old archives in the wild generated with various releases of our code, which we need to be able to reload). Thanks for any help, David.