If I have added google adsense, can I join another text link affiliate program?

you can join anything else as long as it agrees to everyones terms and conditions that you ARE allowed

I also ask this question to google adsense before. Here is their reply:

Thank you for your interest in publishing Google ads on your website. In
regard to your question, we do allow affiliate or limited-text links on
web pages with AdWords ads. Text-based ads that would violate our policy
can be loosely defined as ads that mimic AdWords ads or appear to be
associated with AdWords ads on your site.


So I think you can use other text link affiliate program.

The type of ads that you can't put on the same page as the Adsense ads is similar ads, which are in competition with Adsense. These are ad networks like Clicksor, AllFeeds, Adhearus, etc.

I've seen this thread in 10 of the top sections of the requested section.

Different username, but same question.

It's also on alot of the other top forums as well.

you can use alternative ad if google adsense ad is not availble for some pages that don't have much of text, ex gallery pages or image slide show (unless you have hidden text on page). There is a away to do it while creating google ad link.
line google_alternate_ad_url = "<ALTERNATIVE URL>" is added to google code - as a result alternative affiliate banner or text appears if google ad is not available for some reason.