We had the TRIM service working fine... we are pushing docs out of Salesforce to the TRIM webservice. We were using SSL and operating through a pinhole in the firewall that allowed access only to SF.
Nonetheless we decided to go further and implement client certificates. I will discuss this in another blog entry. The purpose of this entry is to offer suggestion as to how to fix an error 413, that looks something like this:
System.HttpResponse[Status=Request Entity Too Large, StatusCode=413]
So the inclusion of a client certificate had made our callout to the Trim webservice too large? How can we play with the size to see if this is the case? Of course searching returns nothing specific to Trim... but this property sounds worth visiting, especially because it mentions client certificates specifically. Mind you it's not like we were uploading large files. In our case this broke with files of just about any size.
While the UploadReadAheadSize can be set at the command line with appcmd, we used the GUI and bumped it up considerably off the 49152. Here's the IIS details: http://tips4sysadmins.blogspot.co.nz/2012/12/iis-75-uploadreadaheadsize.html
Please look at the S4S release notes for more details.
The latest versions include breaking changes so existing users cannot simply overwrite the existing libraries and expect the functionality to continue working. A recompile of the impacted website projects will be required.