Uncaught exception 'SmartyException'

[patrmich]

Hello,

My shop is built with Prestashop 1.5.6.2.

In an error log file of my server, I can see, from time to time, some lines as follows :

PHP Fatal error:  Uncaught exception 'SmartyException' with message 'unable to write file ../cache/smarty/cache/crossselling/productfooter/..'
in ../tools/smarty/sysplugins/smarty_internal_write_file.php:44

PHP Fatal error:  Uncaught exception 'SmartyException' with message 'unable to write file ../cache/smarty/cache/blocksearch_top/..'
in ../tools/smarty/sysplugins/smarty_internal_write_file.php:44

PHP Fatal error:  Uncaught exception 'SmartyException' with message 'unable to write file ../cache/smarty/cache/ADTM/..
in ../tools/smarty/sysplugins/smarty_internal_write_file.php:44

Would you know what makes this error ?

I thank you in advance for any suggestion.

Patrick