Largest Error Message in 100 bytes
Python 3, \$\approx\$A(A(A(9,9),A(9,9)),A(A(9,9),A(99,99))) where A is the Ackermann function,or limited by RAM

A=lambda m,n:m and A(m-1,n&lt;1or A(m,n-1))or-~n
a='.'*(A(A(A(9,9),A(9,9)),A(A(9,9),A(99,99))))
exec(a)

Don't try it online!
Stole the Ackermann function from here.
More manageable version to demonstrate:

A=lambda m,n:m and A(m-1,n&lt;1or A(m,n-1))or-~n
a='.'*(9999)
exec(a)

Try it online!
Admittedly I'm not certain this approach is arbitrarily extendible in practice.