Full error message:
HMM Def Error: Regression Tree definition expected at line 34/col 10/char 1507 in hmmAdapt/hmmdefs
  ERROR [+7050]  HMError:
  ERROR [+7035]  LoadAllMacros: Get macro data failed in MMF hmmAdapt/hmmdefs
  ERROR [+7050]  LoadHMMSet: Macro name expected
  ERROR [+3228]  Initialise: LoadHMMSet failed
 FATAL ERROR - Terminating program HVite

Fix: 

run HTK 3.2.1 version of HVite

this error occurs when you have an Acoustic Model you adapted with HTK version 3.2.1, but then try to run it against HVite version 3.3

See Ticket #55