The most likely reason the host state got stuck is due to someone logging into the machine during a test run.
Please do the following to reset the ''Host State''.
1.  Log Into  Performance Center Site Admin
2.  Select the ''Lab Management'' Tab
3.  Select the ''+'' to expand the Lab Project tables
4.  Select the table ''Lab_Hosts''
5.  Replace the ''SELECT * FROM LAB_HOSTS'' with the following:
update LAB_HOSTS
set host_runtime_state = 'Idle'
where host_id = 1006
6.  Insure ''host_id'' = the number of the problem host ( see attachment named  ''Host_State_Fix.jpg'')
7.  Press the ''SQL EXECUTE'' button (far right or see attachment named  ''Host_State_Fix.jpg'')
8.  Confirm Host State is back to ''idle'', replace the update LAB_HOSTS... with  SELECT * FROM LAB_HOSTS
9.  Press the ''SQL EXECUTE'' button