We have all seen it....the awesome round tool, uponfailure reportsthat:
Recent changes have caused user-defined transition references to be lost. Changes to either the current feature's geometry or to some other feature have caused the references for user-defined transition (No. 1) to be lost. The affected transitions must have their references redefined.
Recommended actions: Redefine the TRANSITIONS element for the failed feature, and select the Transitions indicated above for redefinition. Reselect lost references.
Riddle me this Batman...why does this happen with a NEW round? With an exsiting round...sure I get it. This is just another case of Pro/E unfinished business.
I don't know if this applies to your situation. I've found that removing features that really have nothing to do with the rounds, really have to do with the edges, which really are lost. I have used used suspend and the problem goes away. It seems to be told its ok by applying this action. This has worked many times for me.