[Luciano]

no idea just gessing...
from the url... modules/vbgallery.php I assume you are using vbadvanced portal.. there seems to an error within the portal software (or the module)
try to disable the module.. and see if the error persists..

if it persists, are you sure you did not update the portal software?

did you change configuration of vbgallery module in portal?

If you have not updated portal software.. there might be some special character or a corrupt image.. that causes an error(or warning) in php.
usually thats why the errors get sent..
try to delete the last upload.. or last post in gallery..

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there are some strange behaviours of the vbadvanced cmps modules..
to debug the module open it in your editor and add exit; at the end.. you should then be able to read the error message..

hope that helps

Luc