Tags sometimes work and sometimes not

I love this component but this error appear sometimes when the people click in my tags:

Warning: array_merge() [function.array-merge]: Argument #2 is not an array in /home/elisur/public_html/turecetadecocina.com/libraries/joomla/application/router.php on line 218

Fatal error: Unsupported operand types in /home/elisur/public_html/turecetadecocina.com/libraries/joomla/application/router.php on line 140

I'm using:
Joomla 1.5.15
PHP version 5.2.9
SQL 5.1.30
Host Hostgator

Components:
Xmap
joomla default SEF

Actually im not using the mod_flexitagcloud because never work always end with the same error

Thanks and wait for you response.

Hi,
The way to solve that easily is to create a FLEXIcontent > TAG menu item in a menu that isn't displayed anywhere.
You can choose whatever tag, it won't appear on the website anyway
Cheers,
Emmanuel.