Correction, I wasn't remembering clearly:
When you declare a var as AnsiString in Delphi, you get the old-style statically allocated string with max length of 255.
The above is wrong. Here's what really happens: when you declare a var as AnsiString, you do get the "huge" string variety. This does not depend on the "Huge strings" compiler switch, since you're explicitly asking for one. The compiler switch only affects declarations of "var s : string;"
But as mouser said, please give a bit more info on your code and the specific error.