MyBatis / Spring - 2 Datasources MyBatisSystemException - Ambiguous Displayed Assertions

Question

I created two data sources in my Spring / MyBatis application. During startup, I get no errors (reading the XML interface and the interface). But when calling the method, it throws the following exception:

MyBatisSystemException: SqlSession operation; The nested exception is java.lang.IllegalArgumentException: selectByPrimaryKey is ambiguous in the Mapped Statement collection (try using the full name, including the namespace, or rename one of the entries)

He does not quite speak clearly about the reason for the ambiguity.