You could try to export your Circuit Maker file into a SPICE Netlist file. Give it a ".cir" extension and then from Multisim go to File >> Open and you will be able to open it...
Saving a schematic in CM and then opening it in MS is not possible, but you can try the SPICE Netlist option... I have never used CM so, please forgive me if by any chance I am assuming that CM can generate a SPICE Netlist option and it ultimately cannot do it.
Nestor
