The most likely explanation is that your Composer history file has become corrupt somehow. Rename the files C:\users\yourusername\documents\fiddler2\composer_scratch.txt and C:\users\yourusername\documents\fiddler2\captures\requests\ComposerHistory.raz and then restart Fiddler.
The most likely explanation is that your Composer history files have become corrupt somehow. Rename the files
C:\users\yourusername\documents\fiddler2\composer_scratch.txt
and
C:\users\yourusername\documents\fiddler2\captures\requests\ComposerHistory.raz
then restart Fiddler.
The most likely explanation is that your Composer history file has become corrupt somehow. Rename the files C:\users\yourusername\documents\fiddler2\composer_scratch.txt and C:\users\yourusername\documents\fiddler2\captures\requests\ComposerHistory.raz and then restart Fiddler.