When you've worked for a couple of hours and then to your surprise you try to save and an evil error message says that you've run out of memory and cant save to central, but you can save your local, try this as a last resource, it worked for me:
1 SAVE YOUR LOCAL
2 OPEN ANOTHER INSTANCE OF REVIT
3 OPEN YOUR LOCAL ON THE NEW INSTANCE -give it a while-
4 IF IT OPENS, SAVE TO CENTRAL, SAVE YOUR LOCAL AGAIN -give it a while-
5 SHUT DOWN THE NON-RESPONDING, FIRST INSTANCE OF REVIT
6 RESTART YOUR PC
7 REOPEN REVIT, OPEN YOUR LOCAL
IF U R LUCKY LIKE ME, THIS SHOULD'VE FIXED THE PROBLEM