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.
Consider a system running CRM Version 188.8.131.526, a customized solution is exported as managed solution and the version number is 184.108.40.206. 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.