Message type: E = Error
Message class:  PPC0 - Messages for PP Confirmation 
Message number: 104
Message text: & is not a resource
Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of messages in the SAP system have a message text, however this is frequently insufficient to comprehend or resolve the problem.
To make things easier, more detailed information is frequently added to describe the issue, how to fix it, and the necessary steps or configuration modifications.
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The SAP error message PPC0104 typically indicates that a specified object (like a resource) is not recognized or does not exist in the system. This error often occurs in the context of production planning or capacity planning when the system is unable to find the resource that is being referenced.
Cause: Resource Not Defined: The resource you are trying to use may not be defined in the system. Incorrect Resource Type: The resource may not be of the correct type or category that the system expects. Inactive Resource: The resource might be inactive or not available for use in the current planning period. Authorization Issues: There may be authorization issues preventing access to the resource. Data Consistency Issues: There could be inconsistencies in the master data or configuration settings.
Solution: Check Resource Definition: Go to the resource master data (transaction code CR01 or CR02) and verify that the resource exists and is correctly defined. Ensure that the resource is active
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