I work for a hosting company that provides Filemaker server 9 & 10 hosting and several of our users are experiencing similar issues to yourself.
We are currently investigating the issue, but have been unable to find the cause so far. I would be very interested to know when you first noticed these problems, who your ISP is, and who hosts your FM database.
by now we have resolved the issue. The basic explanation is - it was a network problem. I had the post also in the Filemaker Pro forum and answered it there:
Concerning your other questions: the ISP and the host of FM Server is in my case the company itself - working for a TelCo company.
I hope our experience helps you!
Thanks for the info & sorry for the delay - long weekend here :-)
The vast majority of our users experiencing issues are using the same ISP, so it does look like its the network. Now I just need to get the ISP to take a look which will be like getting blood from a stone...