SUMPRODUCT not working due to text in column

Hi,

I'm trying to work out how to fix the formula below to take into account and ignore and text entries, while giving me the result of the sum of column K minus the sum of column J. If I delete the text entries, the code works but I need the text entries to stay where they are.

I've attached a sample sheet with fake info to explain whan I'm trying to do.

Cell N28 on the 'MGMT INFO' tab contains the following formula:

=IF(ISERROR(SUMPRODUCT((Sheet01!$K$1:$K$1000)-(Sheet01!$J$1:$J$1000))),0,(SUMPRODUCT((Sheet01!$K$1:$K$1000)-(Sheet01!$J$1:$J$1000))))

Columns J and K on the 'Sheet01' tab contain the Pay and Invoice information for all the work planners for that client that I'm trying to find the difference between. Each work planner has 'Pay' and 'Invoice' also in that column though, one entry per planner which is causing the SUMPRODUCT formula to screw up.

Could ISNUMBER help me out? if so could anyone help me with the correct syntax?

Thanks in advance

Maybe something less complicated:

=SUM(Sheet01!K:K)-SUM(Sheet01!J:J)

=SUM(Sheet01!K:K)-SUM(Sheet01!J:J)
would do that