I started having this problem today too - using Vista Home 32bit. Prior to today ULM has worked fine with no problems.
The library URL is correct: http://ulm.hbyte.net/library.php
I can start to download a book but the book is always broken (brown icon).
Next when I start Uru, I get the error message "UruSetup.exe has stopped working" -and Uru terminates.
To solve the problem of Uru not starting I have to go the /dat directory and delete the relevent partially downloaded files (some 0 bytes), and Uru starts correctly again.
Assume a transient problem with the server or somewhere in between ??