Only some thumbnails updating

[Hana]

I started updating my thumbnails yesterday after installing the modpack, but I've been having problems in that only some thumbnails appear to be updating.
There are some albums in which all thumbnails are updating, some where none of them update and others where only a percentage change.
I've tried changing permissions as suggested in another thread, I've also tried lowering the number of images processed at a time, but neither helped.

[Nibbler]

Did you clear your cache?

[Hana]

Yeah, that was the first thing I tried.

[Stramm]

properly chmod files and folders (644 or 666 files, 755 or 777 folders depending on your setup)

[Hana]

I tried changing the permissions on the files and folders, but this didn't work, and this wouldn't explain why in some folders only some of the thumbnails change.

[Stramm]

have you checked if the files timestamp changed?
and it's no problem to explain why some thumbs in a folder do not update while others do

[Hana]

What's the files timestamp?

[Stramm]

within ftp or shell check when the file has been changed
if it's when you run the admin tools, then OK
if it's somewhen before, then most probably the php user isn't allowed to modify the file -> permission issue

[Hana]

Problem sorted, I'd changed the permissions of the main picture files but not the thumbs 
Thanks for your help!