Hello All!
Recently we had this issue when trying to run a Flow Step (Preview) from a BPF on a custom entity. The Flow was solution aware, in this case, for an Approvals process - we received this error from Sys Admin up to Global Admin. I was able to resolve this issue in the system settings (advanced settings>system>administration>system settings) (this was a QA instance, this setting should be YES in all PROD instances, if it's not - ENABLE IT!)