First, be sure you didn't forget to run upgrade.php after upgrading from an old version and be sure you're not using old templates with a new version (these are two common ways to get parse errors).

If you get a parse error after an upgrade runs, it's possible that a file failed to completely upload -- a partial file will cause a parse error, so try re-uploading the file that the error mentions.

Incorrect syntax in your link importance formula or member rating formula can cause a parse error on submissions/registrations.

On some server setups where output buffering isn't available, errors in template PHP or WSN's template conditionals will cause parse error messages. Usually the cause is incorrect usage, but sometimes unexpected content in template variables used within these areas can be the issue (thus you may have a parse error in one forum but not in another).

Make sure that your debug mode is not set to "suppress errors" and take a look at the information provided to you on the page with the parse error.

If you've been customizing the template, be sure to consult the manual entry on conditionals syntax to see if you are using the wrong syntax on the lines which the error message highlights for you. If necessary, test the default uncustomized version of the template and then slowly reintroduce your changes. If you cannot deduce what the problem is, then copy and paste the content from your screen to WSN support.

It is possible that you could have multiple parse errors. If so, after solving each one you will have to come back and look at the new error message.