PR 4 with no back links - now dropped to PR0!

What's happened?

[ecommerce man]

I've got a site that did have a PR4 across the sites pages. Today the PR dropped to 0! Any ideas why it would do this?

Thanks guys

[thereuare]

Same here... PR dropped to zero in the last few days.

Some will tell you that we are being penalized, but as far as i know my site is clean, so i'm hoping it's just a fluke and will change with the next update.

Given all the tweaking that Google has been doing lately, i think this is quite possible.

[petertdavis]

What do you mean 'no back links'? Nobody links to your site?

[jon80]

If the site has no inbound links the pr4 would have been an estimated pr.

[toolkit]

I didn't think the toolbar estimated pr any more

[dougmcc1]

Aren't penalties reflected by a gray bar?