I've just downloaded electrum-3.0.3-portable.exe from
https://electrum.org and verified the signature with gpg4win-3.0.1, the signature is valid.
SHA-256 of my downloaded electrum-3.0.3-portable.exe: ef5f4bcbb19901bebca743323ae7af48fc349837fcf6a09f9a861c18ff8dbe13
Can you tell us the SHA-256 hash of your file?
Verified the sig and did a sha256. I'm getting the same sha256sum as hatshepsut93:
ef5f4bcbb19901bebca743323ae7af48fc349837fcf6a09f9a861c18ff8dbe13
Where did you download the file from ico_fond? There are lots of fake electrum sites so make sure you only download it from electrum.org and of course verify the gpg sig.
One other possibility is that the download wasn't completed when you verified the GPG sig. When I tried downloading it it took a long time to complete. Looks like their server is overloaded ATM. FYI the file size is 18MB. arihan is working on a 3.0.3 torrent and i'm sure once it's complete they'll put up a link to it on the download page. That should reduce the load on their server.