Indecipherable php warnings when changing page templates

Hi.

I’m working on a wordpress theme, and trying to apply themes to Pages.

I have created a News page. When I try to set a template for it by going to the Page settings, and selecting a template, and then pressing ‘publish’, the admin interface dissapears, and I get a series of php warnings in the browser window.

Nothing else displays except the warnings.

In order to restore the admin interface I hit the back button, and reload. When I do this, get the admin interface, and the php warning appear in the column under ‘Attributes’.

Warning: file(/var/www/hosts/wp/wp-content/themes/mytheme/.#header.php) [function.file]: failed to open stream: No such file or directory in /var/www/hosts/wp/wp-admin/includes/theme.php on line 142

Warning: implode() [function.implode]: Invalid arguments passed in /var/www/hosts/wp/wp-admin/includes/theme.php on line 142

Warning: Cannot modify header information - headers already sent by (output started at /var/www/hosts/wp/wp-admin/includes/theme.php:142) in /var/www/hosts/wp/wp-includes/pluggable.php on line 868

I do not have any files called .#header. Nor do I request such a file anywhere.

What is happening here ?
What are the warnings telling me? How do I recover ?

I’m guessing that I’ve messed up somewhere in the theme creation process. But I can’t tell where.