Did you define the Target Vessel in Mission Editor? Looks like no, because there is no "TARGET_VESSEL" entry in the scenario.
If you want to rendezvous with another vessel, you need to tell Mission Editor the name of it.
To fix this, add the name of the target ("ISS_HD") in the Orbit tab of Mission Editor, and re-save the mission. Then, to fix the scenario above, search for the line "@BEGINSOFTWARE StateVectorSoftware", and after it add a new line " TARGET_VESSEL ISS_HD" (note the 2 spaces at the begining of the line). Now you should be able to rendezvous!