Assuming you are not running incompatible versions of vBond/vManage and CSR1000v, check if you are not hitting https://bst.cloudapps.cisco.com/bugsearch/bug/CSCvp75927
There is a workaround I was made aware of recently which uses the API on the UCS server to make a call directly to obtain the Java KVM console. I have tested this and although you don't get the GUI, you get the full console functionality (turn on/off...