possible reasons for withdrawal

The main reason would be:
Conglin Investment Group can acquire another 4.58m shares at substantially lower than proposed bidding price before its holdings reach the 20% takeover threshold.

What I observed as would make sense as follows:

a) 28/06/2010 Big announcement re Drilling success at CAP Burta BMG JV.
This vital announcement spire Conglin to transfer his shares to his company, ready for the takeover.

b) 01/07/2010 Conglin transferred his shares to Conglin International Invesment Group Pty Ltd.
Smoothly transferred at around 40c, where CAP was around 35c.

c) 06/07/2010 Another announcement re Successful start to drilling at Hughenden Coal Project
This would be another small catalyst for him. Definitely, it strengthens his confidence in CAP.

d) 07/07/2010 & 08/07/2010 Congline Investment Group bought 973k shares at an average price of 43c.

e) 09/07/2010 Congline Investment Group bought 1.3m shares at an average price of 53c. The Group holdings was 19.73%, just close to the 20% takeover threshold.

At 16:00, CAP was Suspended from trading.

f) 13/07/2010 CAP board signed non-binding takeover and indicative letter with Conglin Group.

g) 15/07/2010.
At 14:38 CAP announced 20.8m options were converted into shares. As a result, Conglin Investment Group shareholding was diluted from 19.73% to 15%. It is around 5% (or 4.58m shares) away from the 20% takeover threshold.

After 4hours 22minutes, Conglin Investment Group withdrew the takeover.

The reason would be simple, I think Conglin Group intended to buy another 4.58m shares at substantially lower price before making a takeover bid. It would be saving at least $1.5m cash if Conglin Group acquired another 4.58m at 41-55c.