Within a Dynamics CRM Solution package the major and minor versions are very important. If there is a mismatch in the major and minor version numbers then the solution import will be unsuccessful.
Example:
Consider a system running CRM Version 6.0.0.786, a customized solution is exported as managed solution and the version number is 6.1.0.0. Given the differences in minor version numbers the import will fail.
CRM 2013 has introduced a new feature called down-leveling that allows import of solution with different minor version numbers.
Information Dynamics 