The problem is that the backslashes are interpolated inside perl as a part of the back-quotes `` expression with the result that what gets passed to the shell look like this:

psed -e 's/\///gp' init10CONVERGE.ora > init10CONVERGE.ora_for_unix
[download]

Which isn't going to do what you intended. To avoid that, double escape the regex:

`psed -e 's/\\\\/\\//gp' init10CONVERGE.ora > init10CONVERGE.ora_for_u
+nix`;
[download]

That said, as you are redirecting the output to a file, why are you using back-quotes? system would be more appropriate.