Having a problem with ISNA

I want to get rid of #N/A from a formula. I can get the formual to eliminate the #N/A but then it won't return a value when it should.

This formula works.

=VLOOKUP($B50,INDIRECT("'"&$B$2&"'!$B$2:$K$43"),3,FALSE)

This is the formula I tried with ISNA.

=IF(ISNA(VLOOKUP($B51,INDIRECT("'"&$B$2&"'!$B$2:$K$43"),3,FALSE)),"",(VLOOKUP($B51,INDIRECT(""&$B$2&"'!$B$2:$K$43"),3,FALSE)))

Jim O