adl_adFormat problem

i want to apply DOTA feature in my old wavecom module. It is wavecom fastract wismo inside. 655_09gg.Q2406B, V310.
At first try, it successfully applies DOTA. it can download and install new application from FTP. But at second try, when it tries to format A&D space(because it should clear previous dota file), module hangs. Its led goes off (not blinking nor shining anymore).
Here is my code flow.

  1. Subscribe the cell. adl_adSubscribe
  2. Get cell info. adl_adInfo
  3. If the cell is finalised previously, Unsubscribe the cell then format the cell to clear AD space. adl_adUnsubscribe, adl_adFormat
  4. Connect to FTP server and download the DOTA file onto the cell
  5. Finalise the cell and install. adl_adFinalise, adl_adInstall

Module hangs at 3rd line. What is the possible problems? I couldnt understand the behaviour.

I found a temporary solution. Insead of formatting AD space, i use recompact it after i delete the cell by adl_adDelete function. Now it works OK but i am still curious about why adl_adFormat behaves like this.