This error may result from a missing account in a related customer. 

• In Fourth Shift, go to the Customer Master (CUID) screen for the related customer(s).  SOP users go to the Customer screen.  Make sure all of the accounts in the related customers have values in them.  Those accounts are Accounts Receivable, Sales, Cost of Sales and Freight.
• Rerun the CUSTACCT extract, part of the MGL task to extract the CUSTACCT.DBF file
• Delete the Modcomgl.mc file
• Delete the Modcomiv.mc file
• Delete the Modcomiv.tmp file
• Delete the Modcomsl.tmp file
• Run APMC 
• Rename any modcom mcx files to mc
• Run the applicable module communication process, such as APMC, IVMC or Load Daily Transactions.  Do not run GLMC yet.
• Run the Daily Allocation Tool (Interco.exe) again
• If you choose you may run APMC, GLMC, IVMC and move the Modcomsl.mc to the SAAM folder.  Or you can wait until the next nightly batch and records from the current day's processing will be appended to the mc files.