Sounds not logic but I think there are many cases when a production system is in 46C and (for budget restrictions) the corresponding test system was recently upgraded to ECC 6.0 before doing the same in production.
If not possible, which is the best solution under the indicated scenario?
My best regards.
It may be technically possible to transport between 46C and ECC6, but it is advisable to employ a change freeze.
The main reason for this is that your test landscape now is significantly different from your productive system. It will be very hard to regression/integration test anything fully.
If you also changed from a unicode to a non-unicode system you should be particularly careful.
Custom programs may be reasonably safe to transport, but you have to measure the risk very carefully - particularly in business-critical processes.
Doing transports of SAP-Repairs or enhancements may have very unpredictable results (and may not even be allowed). It will really not be a good idea to transport any SAP objects, as the functionality is likely to have changed during the upgrade.
It may be necessary to create a second DEV/TEST landscape that is 46C in the interim, if you cannot afford a change freeze. However this will require dual maintenance, and can result in it's own set of issues.