AbanteCart v1.4.1 is released.
Clean the AbanteCart error log and try again.Check for latest errors after fail
Did you add "file" upload to the contact us form? If so check that upload folder exist and writable
Upload Directory - directory where uploaded files will be saved. Your directory will be created in _your_site_folder_/admin/system/uploads.https://abantecart.atlassian.net/wiki/spaces/AD/pages/13500486/Forms+Manager
It is hard to answer. Incorrectly configured mail, hosting mail rules, sender (smtp provider).....