#1 That should be absolutely fine.
#2 Thanks for trying. I'm sorry it did not work.
#3 Do the times on the warnings correspond to times that the 'Send' button is clicked? (I know you won't know if visitors to your site try to use the contact form but you could try it yourself a couple of times and note the times down.)
From reading the PHP warnings, it looks to me like your PHP installation is looking for the Ctype extension but cannot find it. It's possible that your site previously used the Ctype extension without any problems but the extension may not have been carried forward after a PHP upgrade. (This is pure speculation on my part but possible, I guess.)
I don't know if this is the reason that your contact form no longer works (did your web host upgrade your PHP recently?) but it would be good to resolve these warnings. I'd contact your web host about them. They should be able to help. I expect they'll likely have seen warnings like this before so they'll probably know the cause and how to fix it.
According to a quick web search "The Ctype extension provides a set of functions that are used to verify whether the characters in a string are of the correct type.". If your PHP installation is triggering this extension after the 'Send' button is clicked but the extension cannot be found (thus returning a fail), then it's certainly plausible that this could be at the root of your problem.
I'd certainly look into getting it fixed (at least to eliminate it from the equation) before moving on to other potential causes.
I know you said that PHP Mail is enabled on your web server but it might be worth checking in with your web host to see if there are any restrictions on this service.
Here are two other things to try:
#1 You could try using SMTP to send the mail rather than PHP Mail. PHPMailer already has the code in place for this but you'll need to modify the Showkase source file which sets the values being sent to PHPMailer to include all the SMTP credentials. Instructions are in this forum post.
#2 If there is a restriction in place whereby mail is not being sent on your web server due to the email address you use not matching the domain of your website, then you could try forcing PHPMailer to not set the Sender address.
(1) Open the 'showkase/admin/plugins/contact/master/contactcore/contact.php' file in a plain text editor.
(2) Change line 88 from:
$mailer->setFrom('mailer'.strstr($siteEmail, '@'), $userName);
$mailer->setFrom('mailer'.strstr($siteEmail, '@'), $userName, false);
I don't know if this will make a difference but it is certainly a quick and easy thing to try.
Please note that the line number above refers to the current version of Showkase (v1.7.6).