PCR problem

[Mr R.J. Parkes]

	I have been trying to PCR a 2kb fragment from a phage clone I am
working with. I have done this succesfully in the past and amplified a
single band using a 2 min extension and 55 celsius annealing temp.
However now that I want to repeat this on the same template I get the
correct size band but with a smear and several faint bands. This smear
is across the size range of 2kb and above. Why am I suddenly getting
this smear when all the parameters are the same as before? 

Thanks Richard