Could you tell me why the address is invalid.

Aye, there's the rub. Usually a duff pointer, all you have to do is find which one (that's a joke, by the way). Thing is that all you are seeing is the result of a memory location being overwritten, not the cause. A needle in a haystack is simple to these kinds of issues. Just because it was failing in the Sybase module does not mean that that module caused the fault - just that it happened to be the area of memory stomped on.

You will not stand much chance using gdb unless you recompile perl and any XS modules with debug switched on (unless you are really good at assembler), and that is not for the faint hearted. Realistically you must try to reproduce the fault and then remove code until it stops happening. Personally I have known bugs like this to have a life of five or six years and never get resolved. Part of the joys of C.

By the way, are you using a reasonably up-to-date version of Perl and associated modules? It might be worth considering an upgrade if you are not.