Recalculating a very large spreadsheet
 

I have a 55MB workbook that takes about 3 or 4 minutes to calc. Therefore, I
use Manual recalculation. I also have 3 supplemental workbooks each of which
is 5MB to 10MB and have links to the primary workbook. Sometimes (not
always), when I have the supplemental workbooks open and I recalc, it can
take up to 15 minutes. While inconvenient, this is not the problem. When
the calc is complete and the status line shows "Ready", sometimes the
workbooks get into a mode where the status line also shows "Calculate"
despite the fact that it just finished calc'ing. Once this happens, it
doesn't matter how mant times I recalc, I can't get rid of the status. If I
close everything, reopen and then recalc, it usually clears.

There are no circular relationships. What might be the issue?

Thanks