any suggestions are welcome.

You might try the "netinstall" approach.

thanks a lot! that did the trick. during upgrade process i noticed some repartitioning/reformating of the internal memory which all the other upgrade methods did not do.

i tried turning to operate a friends rb450g which came with routeros 3.25. a direct upgrade to 6.30.2 did not work out. next step was upgrading to 4.17 and then the router accepted the 6.30.2 upgrade. there is one strange thing i was not able to resolve so far. it seems that the configuration can be...