Message type: E = Error
Message class:  USMDZ3 - Nachrichtenklasse zum UI des User-Interfaces 
Message number: 045
Message text: &1 &2 Change not possible because references exist
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.
The SAP error message USMDZ3045 indicates that a change cannot be made because there are existing references to the object you are trying to modify. This typically occurs in the context of Master Data Governance (MDG) when you attempt to change or delete a master data record that is still being referenced by other records or processes.
Cause: Existing References: The primary cause of this error is that the master data record you are trying to change or delete is still being referenced by other entities in the system. This could include: Other master data records. Transactions or documents that utilize the master data. Relationships or dependencies that have not been resolved. Data Integrity Constraints: SAP enforces data integrity rules to ensure that changes do not lead to inconsistencies in the database. If a record is linked to other records, the system prevents changes to maintain data integrity.
Solution: To resolve the USMDZ3045 error, you can take the
 Get instant SAP help. Sign up for our Free Essentials Plan.
Get instant SAP help. Sign up for our Free Essentials Plan. 
USMDZ3044 &1 &2: Debit/credit signs for group account and contra item must differ
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
USMDZ3043 &1 &2 Breakdown categories &3 and &4 (contra item) are different
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
USMDZ3046 &1 &2: Existing references: group account &3 to account &4
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
USMDZ3047 &1 &2 No accounts assigned to financial statement item &3
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.