Using org 6.25e:

Automatically resuming the clock after an Emacs restart fails under the 
following cases:

1. If org-log-states-order-reversed set to t (default), and a state 
change line precedes the clock line to resume.  Error message is "Cannot 
restart clock because task does not contain unfinished clock".

Example:

*** STARTED test
     :LOGBOOK:
     - State "STARTED"    from "TODO"       [2009-04-09 Thu 13:50]
     CLOCK: [2009-04-09 Thu 13:50]
     :END:

Reason: point is placed at start of state change line and so fails 
looking-at test (org-clock.el:345).

Possible solution appears to be to use the existing function 
org-skip-over-state-notes when looking for the clock line to resume at 
org-clock.el:343.

2. If org-log-states-order-reversed set to nil.  Error message is the 
same.  Reason: point is placed *after* last clock line and so fails 
looking-at test.

Possible solution: test order-reversed and back up one clock entry 
before looking-at test.

I have combined these two ideas into a new function (patch attached).  I 
don't imagine I've handled all of the possible configurations of state 
change entries, log entries, and clock lines, in and out of drawers, so 
this will probably serve more as a basis for a solution than a solution 
itself.

(If nothing else, on org-clock.el:346 there's "\\t" where it should be 
"\t".)

Adam