I was getting and error using a feed import of a csv file.  In syslog there was :Fatal error: Redefinition of parameter $source in /Users/daniel/sites/myproject/wwwroot/sites/all/modules/contrib/feeds_tamper/plugins/default_value.inc

I was getting this error even though I was not using a tamper.

Did a search and found it was fixed in the latest dev file.