Error when using attribute in if-then-else statement for Key Figure

We are attempting to condition the assignment of value for a given key figure with an if-then-else statement that test whether the value for a given attribute tests true or false.  When we use the following syntax, we get the following error The attribute "AVV010" is not available in the output planning level "PERPRODCUSTLOC":  Key Figure 1 = IF(Attribute = "Value", Key Figure 5, Key Figure 2 * Key Figure 3 + Key Figure 4).  The calculation is literally as follows:

     TOTAMNT@PERPRODCUSTLOC = IF(ACCOUNT = "AVV010","HGSAMT@PERPRODCUSTLOC","FIXEDAMT@PERPRODCUSTLOC" + "PERCENTAMT@PERPRODCUSTLOC" + "UAMOUNT@PERPRODCUSTLOC")

Account is the attribute and AVV010 is the attribute value against which we are testing.  If it test true, then we assign TOTAMNT the value in Helper Key Figure HGSAMT, or else we assign TOTAMNT the sum of Key Figures FIXEDAMT, PERCENTAMT, and UAMOUNT.

Thank you for any help you may provide.