Message type: E = Error
Message class:  CRM_IST_SO_MSG - Messages for Package CRM_IST_SO 
Message number: 020
Message text: The main item can only have a component of the type 0101
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The SAP error message CRM_IST_SO_MSG020 indicates that there is an issue with the item type in a sales order or service order within the SAP CRM system. Specifically, the error states that the main item can only have a component of the type 0101. This typically means that the system is expecting a specific item category for the main item in the order.
Cause: Incorrect Item Type: The main item in the sales order is not of the expected item type (0101). This could happen if the item type was incorrectly assigned or if the item type is not compatible with the main item.
Configuration Issues: There may be configuration settings in the item category determination that are not set up correctly, leading to the system not recognizing the item type as valid. Hierarchy Issues: The structure of the order may not be set up correctly, where the main item is expected to have
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