2008 R2, Shared Config, 'Configuration file is not well-formed XML ' trying to read configuration data from file '\\?\C:\inetpub\temp\apppools\*'

I have a working cluster of 2008 R2 servers (8) with shared config on a 2008 R2 filecluster (both config files, and App files) Periodically some of the server stop serving http with:
"The worker process for application pool 'App-name' encountered an error 'Configuration file is not well-formed XML ' trying to read configuration data from file '\\?\C:\inetpub\temp\apppools\App-name\App-name.net.config', line number '3'. The data field contains the error code."

in the eventlog. The last event before this is defrag (at least on the last 2 ocations) There is no failover on the file-cluster. anyone?

nalle