The Islamic Supreme Council of Iraq (ISCI) is the largest voting bloc in the current Iraqi parliment, and they have published a detailed critique of the draft security agreement that has been reached by Prime Minister Nuri al-Maliki and George W. Bush. One unnamed ISCI parliamentarian called the agreement "dead on arrival."
If al-Maliki cannot get the support for it of ISCI, his chief partner in parliament, then the agreement cannot be passed. Too many other political movements, including most Sunnis groups and the Sadrists, oppose the security agreement, for it to succeed in the absence of ISCI support.
ISCI states in their critique that they want to renegotiate key points, but it is unlikely that the the Bush administration has the patience to do this.
This could mean that there is no security agreement by the end of the year, which will place the occupation in legal limbo, as there is a good chance the US could not get an extension from the UN because of the current poor relations with Georgia.