2128986 - SUM Error: Unknown macro FN_WORKPRC

You're performing an Upgrade of your SAP system and hit the following error (regardless of the phase!):

1EETQ399 SYSTEM MANAGER: Instance sapwebdu 01 not found
2EETQ354 Starting system failed, rc="-1"
4 ETQ010 Date & Time: 20140826162355 
1EETQ399 Last error code set is: Unknown macro 'FN_WORKPRC' <------------
System start failed
1EETQ203 Upgrade phase "STARTSAP_TBUPG" aborted with errors ("20140826162355") 

The SAPup_troubleticket.log looks similar to this:

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This trouble ticket was created by SAPup on 20140129122407
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SAPup broke during phase STARTSAP_TBUPG in module MAIN_NEWBAS / Downtime II: Conversion, Main Import, XPRAs
Error Message: Unknown macro 'FN_WORKPRC' <------------
System start failed
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Altough this error is usually seen in startup/shutdown phases, we reinforce it can occur in any phase of the upgrade process.

• SUM (software update manager) release independent
• SAPup release independent

SAPup, software, update, manager, error, message, enhancement, package, EHP, package, support , KBA , BC-UPG-TLS-TLA , Upgrade tools for ABAP , BC-EHP-INS-TLA , Please use BC-UPG-TLS-TLA , Problem