This error will occur when there is no connection ( rfc) between solman and the source system( system for which we are generating xml).
If we check the help log..it ask us to check READ rfc in solman for the source system.
We should check connection as well as authorization check.
Once they are succeded, we need to start a new MOPZ transaction.
We usually think that the MOPZ will go in a smooth way..but we will get the same error because of our mistakes.
With 1 option we need to create READ , TRUSTED & change management rfcs.
and in change mode besides that RFC you will get assign and test button. With that you can define RFCs for respective types.
They will display below ( option 2).
When you define these rfcs.. then only MOPZ will consume the created READ rfc. and you can fix the above issue.