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To fix this, the calling code needs to be updated to use the new parse() API on the Mail::SpamAssassin object. You should check the web site where you obtained that code, to see if they've released an update to support 3.0.0.
If the script in question is part of the SpamAssassin distribution, such as 'spamassassin' or 'spamd', it's very likely that you're not running the 3.0.0 version of that tool, and instead the older 2.x version is still installed on your system, and still in the PATH.
Making the change yourself
If one isn't already there, and you're comfortable making the change in the perl code yourself, here are some quick changes to head in the right direction:
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