Blank compressed pages when the page is not

I am getting blank compressed pages when the page is not, I have a 4 windows 2003 servers farm, it happens only in two of them.

Also some times they merge the content of the pages (i.e. the default page get the content of other)

I don´t have other software on the servers.

My web content is centralized on a NAS and it changes every 15 minutes. I have static and dynamic compression enable, but the 95% of my web content is static and I have detected the problem only on static content.

At the beginning I had this problem on all the servers but I found an article that recommend increase the values of I/O Buffer Size and Compression Buffer Size, this recomendation only works on two of the 4 servers.

thanks for you help