[TYPO3] cwt community include error

[Tom Verdaat]

Dear list,

I'm trying to get the cwt_community extension working, but get the 
following warning one or more times on every page I place the cwt plugin:

Warning: tx_cwtcommunity_lib_common::include() [function.include]: Failed 
opening '' for inclusion (include_path='.:/usr/local/share/pear:/www/
scripts/webshop:/www/scripts/public:/www/t/o/m/tomverdaat.nl/public_html/
typo3conf/ext/cal/res/PEAR/') in /www/t/o/m/tomverdaat.nl/public_html/
typo3conf/ext/cwt_community/res/class.tx_cwtcommunity_lib_common.php on 
line 171

I also get a "cannot modify header information" warning but I know that 
will disappear after fixing this error. Extensive searching using 
support.typo3.org and google did not result in any similar cases.

I've opened the file mentioned in the warning and the warning is caused 
by the include statement of this code block:

/**
*  Merges the $tempColumns from extensions, that extend the table, we are 
currently
*  working on. In case you wrote an extension, that extends the 
"fe_users", then
*  the TCA information for the additional fields will be merged with the 
"fe_users" TCA.
*
*  @param	Array	Extension TCA's that should be merged.
*/
private function mergeExtendingTCAs($ext_keys){
	global $TYPO3_LOADED_EXT;
	//Merge all ext_keys
	if (is_array($ext_keys)) {
		for($i = 0; $i < sizeof($ext_keys); $i++){
			//Include the ext_table
			$_EXTKEY=$ext_keys[$i];
			include($TYPO3_LOADED_EXT[$ext_keys[$i]]
["ext_tables.php"]);

		}
	}
}

Register Globals is turned ON in PHP. I need some help solving this. I'm 
probably missing something very simple but I just don't see it. Can 
anyone help me out here?

Thanks!

Tom