[AUCTeX] auctex preview failed for equation, but works for equation*

[bugger]

I am not sure why. All equation environment are displaying a stopped sign, 
which when I click for error, gives:

<quote>
gs -dOutputFile\=\(_region_.prv/tmp2652fRo/pr1-1.png\) -q -dSAFER -dNOPAUSE 
-DNOPLATFONTS -dPrinted -dTextAlphaBits\=4 -dGraphicsAlphaBits\=4 
-sDEVICE\=png16m -r106.556x105.614
GS>{DELAYSAFER{.setsafe}if}stopped pop/.preview-BP currentpagedevice/BeginPage 
get dup null eq{pop{pop}bind}if def<</BeginPage{currentpagedevice/PageSize get 
dup 0 get 1 ne exch 1 get 1 ne or{.preview-BP }{pop}ifelse}bind/PageSize[1 
1]>>setpagedevice/preview-do{[count 3 roll save]3 1 roll dup length 0 
eq{pop}{setpagedevice}{ifelse .runandhide}stopped{handleerror quit}if aload pop 
restore}bind def [(_region_.prv/tmp2652fRo/preview.ps)(r)file]aload exch dup 0 
setfileposition 18103()/SubFileDecode filter cvx .runandhide aload pop dup dup 
18103 setfileposition 298()/SubFileDecode filter cvx<<>>preview-do
Error: /undefined in --execute--
Operand stack:

Execution stack:
   %interp_exit   .runexec2   --nostringval--   --nostringval--   
--nostringval--   2   %stopped_push   --nostringval--   --nostringval--   
%loop_continue   1753   2   3   %oparray_pop   --nostringval--   
--nostringval--   false   1   %stopped_push   .runexec2   --nostringval--   
--nostringval--   --nostringval--   2   %stopped_push   --nostringval--   
--nostringval--   false   1   %stopped_push   1148   --nostringval--   
%end_runandhide   --nostringval--
Dictionary stack:
   --dict:1159/1684(ro)(G)--   --dict:0/20(G)--   --dict:76/200(L)--   
--dict:102/300(L)--   --dict:19/200(L)--
Current allocation mode is local
Last OS error: 2

Preview-Ghostscript finished
</quote>

equation* and \[ \] works fine though.

--M

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