There are two primary causes and solutions for this issue:
The impeller in the rotating region contacts adjacent (non-rotating) solids. The result is that those adjacent solids are classified as part of the rotating object, and rotate too.
For example, consider a pump analysis. Within the rotating region, an impeller contacts a back plate which also touches the housing. The plate and housing will spin unless the impeller is suppressed.
To resolve this, make sure that no solids touch the rotating solid part. There should always be a layer of fluid between any rotating and non-rotating solids within a rotating region analysis. Alternatively, suppress any solid parts embedded in a rotating region that also contact static, non-rotating solids.
One or more static (non-rotating) parts are assigned the same material as the impeller in the rotating region. The result is that these static parts also rotate. For example, if a material named “Aluminum” is assigned to both an impeller and the static housing, both rotate.
To resolve this, assign unique material names to meshed solids within a rotating region. Assign different materials to parts that rotate and to parts that do not. The material properties can be identical (if needed), but the material names should be different.