A damaged corpus file can cause SpamSieve to crash at launch. Corpus file damage can be caused by crashes or disk errors.
There are several ways that you can fix this. First, quit both your mail program and SpamSieve. Then:
If you have a backup from before the damage occurred, you can replace the file:
/Users/<username>/Library/Application Support/SpamSieve/Corpus.corpus
with a working copy. See the How can I open the Library folder? section for how to find this file and this page for how to restore files via Time Machine.
You can have SpamSieve reset the corpus for you:
Open your Applications folder and select SpamSieve.
While holding down the Command and Option keys on the keyboard, double-click the SpamSieve icon.
Note: If holding down the Command and Option keys does not work for you, you can instead enter this command:
defaults write com.c-command.SpamSieve ShowResetAlert YES
into Terminal and press Return before launching SpamSieve.
Click the Reset Corpus button in the window that pops up.
Re-train SpamSieve as described in the Do an Initial Training section.
You can reset the corpus by deleting the file manually:
Open your Library folder. See the How can I open the Library folder? section for how to do this.
Find the file:
/Users/<username>/Library/Application Support/SpamSieve/Corpus.corpus
Inside Library, find the Application Support folder. Inside that is the SpamSieve folder. Inside that is the Corpus.corpus file.
Drag the Corpus.corpus file to the trash.
Re-train SpamSieve as described in the Do an Initial Training section.