Not working anymore on last two posts

I Noticed a problem with the plugin. I have a custom page where I retrieve the category permalink for each post with PHP. On the last two posts on my blog this displays “Uncategorized”, even though I have set a permalink for both of them (and the permalinked category is correctly displayed in the post edit window). In the database for older posts under meta_value in the postmeta table I see only a number, like 3 or 492. The two new newer posts display a:1:{s:8:”category”;s:1:”3″;} and a:1:{s:8:”category”;s:3:”463″;}

Is there an error in the plugin? THanks in advance,
Joff