reporting services - SSRS - Complicated expression for derived column, gives error -

i'm building ssrs report in bids. need give end-user ability filter report based on approval status. however, there 4 separate approval columns each row - we'll call them approvala, approvalb, approvalc, , approvald; status of each determines overall status of row. each of 4 can have 1 of 4 values - approved, in progress, rejected, or n/a. approach has been create derived column based on whether 4 columns combination of approved , n/a or rejected , n/a, or whether in progress in of columns; filter based on derived column. every time run report, though, error message:

"[rsruntimeerrorinexpression] value expression field 'approval_status' contains error: input string not in correct format."

as far can tell, query should work, pretty convoluted , i'm still new ssrs. advice wonderful. expression derived column below:

=switch((fields!approvala.value or fields!approvalb.value or fields!approvalc.value or fields!approvald.value) = "accepted" or (fields!approvala.value or fields!approvalb.value or fields!approvalc.value or fields!approvald.value) = "n/a", "accepted", (fields!approvala.value or fields!approvalb.value or fields!approvalc.value or fields!ispfapproved.value) = "rejected" or (fields!approvala.value or fields!approvalb.value or fields!approvalc.value or fields!approvald.value) = "n/a", "rejected", (fields!approvala.value or fields!approvalb.value or fields!approvalc.value or fields!approvald.value) = "in progress", "in progress") 

something might work , replicate desired logic:

=switch(   (fields!approvala.value = "accepted" or fields!approvala.value = "n/a")     , (fields!approvalb.value = "accepted" or fields!approvalb.value = "n/a")     , (fields!approvalc.value = "accepted" or fields!approvalc.value = "n/a")     , (fields!approvald.value = "accepted" or fields!approvald.value = "n/a")     , "accepted",   (fields!approvala.value = "rejected" or fields!approvala.value = "n/a")     , (fields!approvalb.value = "rejected" or fields!approvalb.value = "n/a")     , (fields!approvalc.value = "rejected" or fields!approvalc.value = "n/a")     , (fields!approvald.value = "rejected" or fields!approvald.value = "n/a")     , "rejected",   fields!approvala.value = "in progress"     or fields!approvalb.value = "in progress"     or fields!approvalc.value = "in progress"     or fields!approvald.value = "in progress"     , "in progress" ) 

you've got syntax error; like:

(fields!approvala.value   or fields!approvalb.value   or fields!approvalc.value   or fields!approvald.value) = "accepted" 

will cause error each of clauses needs evaluate boolean; can't nest fields that.