Trash will not delete from trash folder! What can cause this effect?

Various possibilities. Try some of the hints from The X Lab.

Were there any error messages or alerts, and if so, what were they.

u can actually force it to delete, oviously i assume you dont have the application or data etc open neware else?

try restarting your computer, go into finder close all your open applications etc, servers, **** even clear your data in your web browser, do a disk utility check and verify your drives and repair em if nessicary.

as chamar suggested look at http://www.thexlab.com/faqs/trash.html

i had the same problem before but with a good 5-10 minutes of googling i was able to solve it..

best of luck