Potlatch Corp. said it expects to report non-recurring charges of about $9 million before taxes for the fourth quarter of 1985 . . . Ashton-Tate reported that it is notifying distributors and retailers of a disk manufacturing error in initial copies of dBASE III PLUS, serial numbers 2500001 through 2533960 . . . Two companies controlled by the Belzberg family of Canada reported in a Securities and Exchange Commission filing that they have raised their stake in H.H. Robertson Co. to 20.9% from 17.9% . . . Venezuela cut crude oil prices by between 80 cents and $1.30 a barrel, retroactive to Jan. 1.