Can you hurt your PR by blocking pages on robots.txt?

Can you hurt your PR by blocking pages on robots.txt?

Recently I have been working hard to reduce the number of errors for my website as shown in Google Webmasters account under Diagnostics, Content Analysis. At the moment, I’m seeing many errors under “Duplicate meta descriptions” and “Duplicate title tags” consisting of the same URL but with the tracking parameters we use for tracking conversions on external traffic sources.

For example:
http://mywebsite.com/page1.html
http://mywebsite.com/page1.html?source=abc

My orginal solution was to add this entry to my robots.txt:
Disallow: /*/?source=*

This way I can More