Solver question
 

When using Excels standard solver and assuming problem is linear, the
solver says it is not and can not solve the problem because it is too
big
Then after replacing the SUM function with cell1 + cell2 + cell3 etc.
instead of SUM(cell1:cell3) it is linear and the solver works. Where
can I get information (TIPS/TRICKS) on building criterias the right way
to standard solver? Wich "non good excel functions" can be written
another way.
Thanks!