Nesting IF statements

I'm trying to nest if statements that also include "and" and "isblank" factors. The following formula isn't working, and I'm not sure if it's because of my use of isblank or lack/placement of parentheses.

=if(and($h$10<>0,$i$10<>0),index(JointTable2008,Match($h$10,Spouse1,0),Match($i$10,Spouse2,0)), if(and($h$10<>0,(isblank($i$10)),index(SingleTable2008,Match($h$10,Single,0)), if(and($i$10<>0,(isblank($h$10)),index(SingleTable2008,Match($i$10,Single,0)), if(and(isblank($h$10),($i$10)),”Not applicable”,”ERROR”)

I'm sure I don't have enough parentheses at the very end, but not sure what else is wrong.