ERR CONNECTION REFUSED for some webs

[Guest]

[abnet3pm]

Hello
I have internal problems with the Pcs behing the endian recently.
In morning ( 8 am to 9:45 am) the PCs can't find specific pages, not all, only some ones.
This pages are in tha white list  but  the browsers shows the messages ERR CONNECTION REFUSED.
In the PC that have the problem , i can do a ping and traceroutr without problem
In a PC bypassing the endian , a I don´t have this problem.

The solution that i applies is reset the endia server several times  and these pages will able again. 
I disactivated all the upgrades, I put a snifer and there are not high traffic in the lan
The server is not saturaded, the memory es 40% free and the procesos are low than 20%

Its weird because , out of the endian , I can see all pages  but behind  I can´t only somesone that the users needs

Please , some one have the same trouble,?? any idea?

Thanks

Joseph