No-one can force an error of any sort, it's not possible. The only person who can make the error is the batsman, not because he's been fooled by a change of pace or length, but because he's got something wrong.
That he's got something wrong, and that 4 batsmen have got something wrong in the same innings, reflects nothing on the skill of the bowler.
Not on the batsmen's part, no, but on the bowlers it's nothing else.
For one thing, it wasn't the bowlers that forced the batsmen into their shell.
Because there are anomalies in all trends. McGrath isn't the only one, Pollock is exactly the same; Flintoff has had similar experiences since the Sri Lanka tour (though he didn't before); and there are plenty of others who get similar situations over short periods. For most, though, it's short-lived, and things even themselves up so that the figures accurately reflect matters.
But how many times have we seen batsmen not get frustrated because of slow scoring-rates? Infinately more than we have seen them get frustrated.