I have become aware that I am no longer receiving emails from the contact form or for registrations. It did work in the past and I'm not sure how long its actually not been working for, maybe more than 6 months. I just thought I was being ignored

The email settings are as they have always been, defaulting to use sendmail, ie nothing in the boxes. Other scripts are able to send mail so I'm pretty sure the mail side of the server is ok. I've just updated from 1.5.22 to 1.5.24 to make sure there are no files missing but no difference.
I've enabled debug mode and I see the flowing errors when I try and enter a contact messages
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/contact.php
Notice line 241: Undefined index: captcha_field_mandatory
Notice line 257: Undefined variable: highlightFieldCSS
Notice line 271: Undefined variable: expand_array
Warning line 271: in_array() [function.in-array]: Wrong datatype for second argument
Notice line 299: Undefined variable: expand_array
Warning line 299: in_array() [function.in-array]: Wrong datatype for second argument
Notice line 324: Undefined variable: expand_array
Warning line 324: in_array() [function.in-array]: Wrong datatype for second argument
Notice line 353: Undefined variable: expand_array
Warning line 353: in_array() [function.in-array]: Wrong datatype for second argument
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I don't know if these are relevant or not.
On entering the details in the contact form and hitting 'GO' I get a blank screen.
Any suggestions welcomed. Debug mode is still enabled and the gallery is at
http://www.drookitagain.co.uk/coppermineOther than this the gallery appears to be working ok.
Donald