Verify that your Solr user account has Log On as Service rights if an error occurs while installing Solr stating that the Credentials that were entered are not valid. Please verify the following: The domain, user name and password are correct .

To verify that your Solr user account has Log On as Service rights:

1. On the Solr server go to Administrative Tools > Local Security Policy . A new window appears.
2. Go to Local Policies > User Rights Assignment .
3. Double click on the Log on As a Service policy.
4. Add your Solr window's user account to the policy.

http://technet.microsoft.com/en-us/library/cc739424%28v=ws.10%29.aspx