There is a known issue where nodes in ISM repository prevents ISM operations on users machine where RAM Concept is installed with Structural Synchronizer CE V11.
Workarounds:
There are two ways to circumvent this error.
The first and simplest way is to downgrade to Structural Synchronizer CE V10.
The second approach is to ensure the ISM repository is devoid of all nodes, and ensure "Recompute Nodes" is unchecked in RAM Concept. See below video of this in action for REVIT 2020:
1 "New from ISM Repository'"
2 - When Change Management mode in iTwin Analytical Synchronizer shows up -> Reject all nodes.
3 - Update on the Synchronizer
4 - In Ram Concept uncheck recompute nodes tick box