This error may result from a missing field in the AR_ACCTS extract 

• In Fourth Shift, go to the Data View Definition (DVUD) screen for AR_ACCTS
• Ensure the fields selected are CUST_ID and ACCOUNT_NO
• Rerun the AR_ACCTS extract, part of the MGL task to extract the AR_ACCT.DBF file
• Delete the Modcomgl.mc file
• Delete the Modcomsl.tmp file
• 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.