Message type: E = Error
Message class:  WI - BPT Workflow: Messages from Info System 
Message number: 126
Message text: Enter a key
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.
Unfortunately, there isn't any extra information in this error notice.
First, use our AnswerBot below to get a possible cause and solution (requires a premium subscription).
Also, review the in-depth Common Questions & Answers listed below; you could discover a solution there or be able to connect with others who have faced similar challenges.
You can also try searching the SAP support portal (support.sap.com) but you need a special user ID to access it. It is possible that an SAP support note exists that provides additional details about the mistake or even steps for fixing it.
SAP Error Message: WI126 - Enter a key
Cause: The error message WI126 - Enter a key typically occurs in SAP Workflow when a required key field (usually a unique identifier or primary key) is missing or not entered in a workflow step or container element. This key is necessary for the system to identify the specific object instance the workflow is supposed to process. For example, if a workflow step expects an object key (like a Purchase Order number, Material number, or any business object key) and it is not provided or passed correctly, SAP will prompt this error. When does it occur? When a workflow step is triggered without the required key. When the workflow container does not have the necessary key value. When the binding of the workflow container element to the object key is missing or incorrect. During workflow start or task execution if the key is not supplied.
Solution: Check Workflow Container Bindings: Go to the workflow
 Get instant SAP help. Sign up for our Free Essentials Plan.
Get instant SAP help. Sign up for our Free Essentials Plan. 
WI125 Selected object type must support interface type 'IFFIND'
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
WI124 No workflows found that can be started
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
WI127 The selected step cannot be displayed in the current client
What causes this issue?  The step selected is client-dependent and is different to the current client.System Response  The step or the workflow for th...
WI128 Task '&1' not used in any workflow
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
Click on this link to search all SAP messages.