[TYPO3-english] fatal error with update from version 4.5.10 to 4.7.7

[Muriel le Pair]

Hi,

when trying to update  website from version 4.5.10 to 4.7.7 I get the 
following error:

Fatal error: Declaration of t3lib_cache_frontend_StringFrontend::set() 
must be compatible with that of t3lib_cache_frontend_Frontend::set() in 
/home/website/domains/website.nl/public_html/typo3_src-4.7.7/t3lib/cache/frontend/class.t3lib_cache_frontend_stringfrontend.php 
on line 0

The odd thing is, I transfered the complete website + database to a 
testing environment. But I can't reproduce the error there.

Does anybody know what triggers this error, or how to prevent it?

--
kind regards,

Muriel le Pair