File Upload Error

Using the documention in the help section I have loaded the code to enable file uploads.
Initially it worked, but after some minor coded changes (not relating to the upload) we now get the message “There was an error uploading the file.” & “One or more fields have an error. Please check and try again.”
If I remove the file upload code the form works.
The code used in the form is
<label> Your name
[text* your-name] </label>

<label> Your email
[email* your-email] </label>

<label> Subject
[text* your-subject] </label>

[file your-file]

<label> Your message (optional)
[textarea your-message] </label>

[submit “Submit”]

I have added [your-file] to the mail attachements & file uploaded is 20kb
I have uninstalled the plugin and reinstalled and still get the problem.
Can anyone suggest anything?

The page I need help with: [log in to see the link]