mac to mac facetime calls

I bought one used MacBook and one refurbished mac book both are the same year 2009 and models A1342. one has been upgraded to run Yosemite and the other is running maverick . I had both these machines using facetime together. both would make successful calls back and forth with each other and both received calls successfully. now the one running Yosemite cannot make a call to the one running maverick. the one running maverick can call the one using Yosemite and you can accept the call successfully. however the one running Yosemite will not call the one running maverick. it just rings indeffinantly from the one on Yosemite. it never connects. I tried to put them on the same wifi net work that didn't change anything.

I saw something on here that said something about icloud. the one with maverick is signed into icloud. is this the solution or is there something else happening? . nobody is blocked on either machine. why would one suddenly stop making successful calls to the one that is making successful calls.?

the trouble shooting q&a doesn't have any questions relating to this. very frustrating.