The story...

FEMA's BPAT, who wrote the WTC Building Performance Study, were not given access to Ground Zero. Apparently, they were not even allowed to collect steel samples from the salvage yards. According to Appendix D of the Study, "Collection and storage of steel members from the WTC site was not part of the BPS Team efforts sponsored by FEMA and the American Society of Civil Engineers (ASCE)."
http://911research.wtc7.net/wtc/groundzero/cleanup.html

Our take...

Can this be true? The obvious first check is to visit Google, and search for the phrases "building performance assessment team" "ground zero". 

"At the beginning of October, the team visited the collapsed and damaged buildings at Ground Zero and over a period of six days collected a significant amount of data on building performance under extreme conditions."
Original link broken - try here

"Team members toured what was left of the 16-acre World Trade Center Plaza, interviewed officials and eyewitnesses, and examined remnants of fallen structures at the Staten Island landfill and at salvage yards. Steel samples were cut and catalogued for further study, and some were taken back to WPI for analysis (see The "Deep Mystery" of Melted Steel)".
www.wpi.edu/News/Transformations/2002Spring/fall.html

"The investigation consisted of visiting Ground Zero, a survey of the WTC site, land-fill and steel recycling centers, review of videotape records, eyewitness accounts, interviews with building design teams, and analysis using computer models".
www.engr.mun.ca/~csce/Page_files/events/upcoming/National_lecture_2003.html

No block on access here. The worst you can say is that access was delayed, but then is that so surprising? With rubble everywhere and fires burning until December (www.newscientist.com/article.ns?id=dn1634) it would take time to make the site safe.

Robert F. Shea of FEMA gave related testimony to the House of Representatives on March 6th, 2002:

Because of the importance of the rescue effort at the World Trade Center complex, it was clear that information would have to be gathered without interfering with response and rescue activities. Based on this fact, the FEMA-ASCE team first visited the site on October 6, but gathered information from others who had been on-site before this date. This information included plans, photographs, videotapes, eyewitness accounts from rescue workers and reports from the New York City Department of Design and Construction. In additiondifficulty in finding material such as steel, the Structural Engineers Association of New York, in support of the City and as a formal member of the BPAT, located and identified specimens of steel for use in future studies. FEMA is coordinating with NIST to make sure that these specimens are properly stored and available for future testing. Also, it is important to note that there are, literally, thousands of plans, specifications and other documents for the World Trade Center.  Although it took some weeks to obtain the plans, the owner’s were fully cooperative with our requests.
http://www.house.gov/science/full02/mar06/shea.htm

However, it’s been recognised that even in circumstances like those at the WTC, access should be provided more quickly, and in 2002 the National Construction Safety Team Act was introduced.

"The new legislation would give future building performance study teams early site access, subpoena power and up to $25 million per year".
http://www.asce.org/pressroom/news/display_press.cfm?uid=1058