The ISFDB search by "book" (i.e. title and author) has changed. I don't know how long ago, I've never tried it before, since either title or author usually does the job.
This seems to work instead:
Code:
http://www.isfdb.org/cgi-bin/adv_search_results.cgi?USE_1=title_title&OPERATOR_1=exact&TERM_1={title}&CONJUNCTION_1=AND&USE_2=author&OPERATOR_2=exact&TERM_2={author}&ORDERBY=title_title&START=0&TYPE=Title
Or switch out "exact" for "contains".