A couple of dats ago, GPUGRID announced this in their forum and even directly in BOINC manager:
 

 
Those WU's came With a problem.
 
One sentence in the Client_state.xml make them fail.
The problem is fixable, but we must edit this file before it uploads.
Please read this thread over at GPUGRID   
 
Not cool to see two 780ti's chew for 30hrs, then the wu's end in error or just vanish.
 
 

bcavnaugh
I was hopping to get a few!

Ya, one must go "Fishing" lol
The wu's comes at random together With the long tasks, so if you have unchecked all other tasks but long ones, you increase your chanches to get Lucky.
 
The first wu's has began to tick in. Those wu's are baddies, but With the heaviest hardware out there, one will get rewarded.
 

As you can see from the numbers provided, one WU deal 500k, while another deal 600K
This 4. 5 or 600k is determined by turnback time.
 
The upper one, the 500k Wu was done With a 780Ti SC. 23,8hrs of crunching, was rewarded 21k credits pr computation hour. Not shabby, but not sensational either.
 
The lower one, rewarded 600k. This one was done in 20hrs by a 980, and it gave 30k pr hour.
That reward even beat devlin's PrimeGrid Sieve's at 25k pr hour 
 
For comparison, the mid WU, a "Normal Long WU" was rewarded 187.550points.
This one was also done With a 780Ti, and was rewarded Close to 16k pr hour, which is par.
 
I have reasons to believe they have fixed the "Client_State.xml" error.
I went trough some of the latest files, and it seemed the Wu comes together With correct files now.
 
Happy Fishing gentlemen