This techincal note outlines an issue when trying to add objects into a package via the Add button in the Import Package window in Strategy Object Manager. The object ID might differ however the cause is the same.
SYMPTOMS
When adding objects to a package in the Import Package wizard by hitting the Add button in Strategy Object Manager, the following error is returned:

Object with ID '5FF2A9F1A45143FD8F4A3B4B2FE14415' and type 8 (Folder) is not found in metadata. It may have been deleted.
Contact Strategy Technical Support for further assistance with this issue.
Drag the objects needed for the package from the main Strategy Object Manager window and drop them in the Import Package wizard.