Some of the items that were modified while disconnected cannot be automatically checked out, possibly because these items ...

Some of the items that were modified while disconnected cannot be automatically checked out, possibly because these items are exclusively checked out by someone else. You must manually check out these items when they become available.

However, the source control provider for these items probably cannot merge your changes correctly with the latest versions when they are checked out. Unless you do the merging without using your source control system, you may lose data.