The meaning of the warning message is – same load case cannot be present in two separate types of load envelopes. If same load case is specified in different load envelopes, program considers the last envelope type for those load cases present in both the load envelopes. For example, consider the following load envelopes --
DEFINE ENVELOPE100 110 120 121 ENVELOPE 1 TYPE STRENGTH100 110 125 126 ENVELOPE 2 TYPE SERVICEABILITY
For these load envelopes, load case 100 and 110 is present in both the load envelopes. So these load cases will be treated as service load cases considering the load envelope type of the last load envelope.
It is required to define separate load cases in separate load envelopes.