UPDATE query is not "an updateable query"

Question

I get "Operation must use an updatable query"

when I try to run this;

UPDATE survey 
INNER JOIN assay_depths 
ON survey.hole_id = assay_depths.hole_id 
SET survey.depth = [assay_depths].[max_depth]
WHERE survey.depth = -1;

The problem is in the WHERE. Something to do with the '-1'?

UPDATE:

hole_id         azimuth   depth    dip
230DD93_L43         312    0       -78
230DD93_L44         318    34.2    -82
230ER99E33          315.5      -1      -65
230ER99E34          337.5      -1      -65