There is a bug in 1.2.6 to do with the new auto refresh option. If you enable this option you may get a .NET error message appearing regularly.
There is a fix for this in test build 1.2.7, http://pmem.uk/joinfs/development.html, alternatively you can just disable that 'auto refresh' option for now.
The stable build of 1.2.7 will be released on Monday 4th September.
Apologies for any inconvenience,
Peter