Large RSS feed breaks code

I have several different calendar feeds that all work fine when delivered in small amounts but choke up with a large amount of items.

The links in this chain all appear sound: the calendars are generated in iCal, published to our private webdav server and RSS generated through php ical. The feeds all work fine in Firefox feed reader and non-WP websites, regardless of size. Code all appears sound as well.

I’ve played with settings for memory_limit, post_max_size and upload_max_filesize, trying to get past what appears to be to sort of max limit – memory, character, item? – with no luck.

The error is get is:
Warning: array_slice() expects parameter 1 to be array, null given in /usr/local/www/data/wordpress/wp-content/themes/structure/calpage.php on line 49

Warning: Invalid argument supplied for foreach() in /usr/local/www/data/wordpress/wp-content/themes/structure/calpage.php on line 53

But my thought is that this error is a red herring; it seems to indicate an error in the code which, if that were the case, would hang up on anything.

Obviously, I’m stumped. Any thoughts or suggestions appreciated.
Thanks,Stace