Invoice won't post and errors with "Unbalanced Distribution"

SOLVED

Our Customer Service team started receiving this error when posting some invoices: "CI2200860 ZSIHI : Unbalanced Distribution 4 (ZSIHI Line 410)" and I'm not having any luck resolving it. I have run GTEST to check the posted amounts and they balance. I have tracked down the script for ZSIHI (I think, there are two possibilities) and checked line 410 on both which either refers to a CCE9 field or an AMT field (code is below) neither of which seem to be possible sources for the error. I've got a ticket in with our reseller but thought I'd post hear while waiting for them to get back to me. Any help would be appreciated.  

WMGAUZSIHI 410 is part of a CASE statement and reads
When "CCE9"
ZONE = [F:TB2]CCE(8)
Checked SINVOICE and SINVOICED tables for CCE9 > field is empty

WMGAVZSIHIA line 410 is part of a CASE statement that reads
$EVAL230
Case EXPR
When "AMT"
ZONE = [F:TB1]DTAVATAMT(7)

Thanks

Paul