Try 37 deg C for 4 hrs with 1 u of BRL ligase and buffer. (The buffer has PEG in it and if you need more details you can get it from BRL). The other modification you should carry out is to blunt-end before gel purification (ie immediately after RE digestion See Pages F2-F5 in Sambrook et al., (1989). Hope thi helps, Priyal de Zoysa.