First of all, the circumference equally exactly pi times the diameter is only true of perfect circles (which only exist in theory).  Try making a circular object yourself, and you'll find that the circumference will only be roughly pi times the diameter.  It may be 3 times as great.  It may be 3.3 times as great.  Especially if you make the object without using any more measuring tools than Hiram used (his measuring tool was likely his forearm, since that is how cubits were measured).

Also, pi equalling 3.14 itself is an approximation, as is 3.  Why is 3.14 an appropriate approximation, while 3 itself is not?  No one has ever written, or even calculated, the exact number for pi, since there is no exact number (it would be eternal).  Three is correct within 95% of the actual value, while 3.14 is correct within 99.9% of the actual value.  So who decides what kind of rounding off is close enough?  Do the critics really expect this passage to end with, "....and a line of 31.4159265 (etc, etc.) cubits did compass it round about"?

Everyone approximates.  When a financial report says a company is worth 10 billion dollars, do people complain that the company is actually worth $9,824,023,855.03?  Even those pointing out the 'error' here are approximating in whatever value they express for pi.  There are many examples in the Bible of obvious approximations.  For example, the populations given in Numbers Chapter 2 always end with even hundreds, or in some cases fifties.  Are we expected to believe that each population came out to such exact numbers?  Nope, that is yet another example of approximations in the Bible.

Approximation is not considered an error, so there is no error in this passage.