Old gallery pics not smush it – zlib compression problems

Hello guys, how are you?

I am having some problems to smush my 10.000 pictures – I tried to bulk it but it keep saying “invalid format. only jpg or png format are available” – I turned on the debug mode and got the msg below:

[18-Jun-2016 15:58:04 UTC] PHP Notice: ob_end_flush(): failed to send buffer of zlib output compression (1) in C:inetpubwwwrootviajologoexistowp-includesfunctions.php on line 3549

I am using the W3 Total cache plugin, I turned it off to see if something change, but no.

All new files (jpg or png) gets smush normally.

The problem it is just about the old gallery – I tried the smush pro but got the same problem and could’t work out…

Hope you can help.