Description
A schema lock cannot be acquired because a lock already exists.
More than one user may be viewing and editing the same data at the same time. This can include being used by services.
To complete the operation, the application must obtain an exclusive lock. This means that the application must be able to assume that the schema is fixed and is not changing at any time that you are working with its contents.
Solution
Ensure that you are the only one using the dataset and retry the operation.