The content access permissions need to be rebuilt. Rebuild permissions?
I cannot give you a full answer. Your answer is specific to your website.


  "The content access permissions need to be rebuilt. Rebuild permissions"
  what is this means?


From some Drupal 6 documentation:


  Rebuild Permissions If the site is experiencing problems with permissions to content, you may have to rebuild the permissions cache.
  Possible causes for permission problems are disabling modules or
  configuration changes to permissions. Rebuilding will remove all
  privileges to posts, and replace them with permissions based on the
  current modules and settings.
  
  Rebuilding may take some time if there is a lot of content or complex
  permission settings. After rebuilding has completed, posts will
  automatically use the new permissions.


You then asked:


  Can I go for Reubuild Permission?


Sure. This process can take a long time though for a site with many nodes and content.


  Will it cause any problem for current modules?


Depending on your situation and the new modules you've installed that are changing how content permission is being assigned rebuilding permissions may or not affect your users. You must first verify what modules are affecting the content permissions and be sure you've assigned appropriate permissions to specific roles that may be using them. It is your responsibility as site owner to be aware of module dependencies.