Thank you for your post, and I must apologize for the late reply.
To make things worse, I don't have an answer why your PHP write permissions are blocked.
Don't worry about removing the SLSocket55.trc file. You do what you have to do to get it running. The bottom line is that you shouldn't have to do that. I would also stick with IIS on Windows, since that is what is certified. Switching to Apache may cause some other problems.
Can you be a little more specific about "lots of people accessing this database". Tens? Hundreds? This could have something to do with it, but difficult to determine.
When the PHP write permissions are blocked, does the server continue to run? That is, are the databases still up and running? Can other FileMaker Pro users still access the database files?
When you start to notice this, what were you doing just before this occurred? I know this was posted a long time ago, but I'm just searching for any kind of common link to explore.
Tomcat is used to communicate between the server and web publishing engine, so those log files may be helpful in determining the cause. You can find those log files at:
This may provide some insight to why this is occurring.
If you remember any other details, even if minute, it may help with narrowing down a possible cause.
Again, I apologize for the late reply.