I tested building the trees, and grass. To remove them edit something near by, rotate your camera under the tree or grass and click the bottom. Once you have the tree or grass in edit mode move it to be sure then delete it.
I just had the same issue with my Second Life Account! Literally just got it fixed today! I use Webroot and I contacted my tech support team and let them remote acess in to my machine come to find out its a simple setting in the privacy settings of webroot! Go into advanced settings privacy next to your viewer select Protect because Deny is auto checked hit save and you're done. Good Luck:matte-motes-big-grin:
-Ezmerelda Optera