I thought you were referring to the recent negotiations and timeframe that led to the most recent UN Security Council Resolution (UNSC Res. 1929). In the not so recent past, Iran did temporarily suspend enrichment activities. Unfortunately, during that brief period, it did not provide the full transparency that was needed by the IAEA to address international concerns related to Iran's nuclear activities. In fact, the IAEA consistently raised issues about Iran's lack of transparency during that period and immediately afterward, e.g., in its February 27, 2006
report.
Moreover, at times Iran has acted in bad faith e.g., failing to make material disclosures to the IAEA. Most recently, Iran disclosed construction of the Fordow enrichment facility in Qom in September 2009 even as it had been required to do so much earlier. On that issue, the IAEA
declared, "Even if, as stated by Iran, the decision to construct the new facility at the Fordow site was taken in the second half of 2007, Iran’s failure to notify the Agency of the new facility until September 2009 was inconsistent with its obligations under the Subsidiary Arrangements to its Safeguards Agreement."
The combination of a persistent lack of Iranian transparency, periodic bad faith, and continuing enrichment activities have not only prevented the IAEA from completing its work, it has caused international concerns about the nature of Iran's nuclear activities to increase over time.