Juddering and skipping with Sonar XL amd MC 4

Hi All,
 
I have a big problem with cakewalk and I need some help big time.
 
I use Cakewalk to edit midi files before using them as backing tracks when I am playing live. I save the file when I have edited them and then group them together in set lists when I go out and do my thing.
 
Up until very recently I used Sonar XL to do this but It started to cause trouble, when I start a file running, as a sigle file or as part of a set list, the program judders and skips for the first few seconds, after 4-5 seconds it calms down. As you can imagine this causes major problems when I am trying to play live. The start of every song is like a dogs dinner mixed with a free form jazz drummer on acid.
 
I thought I would sort the problem by installing a newer version of cake walk (Music Creator 4) but the problem has persited.
 
I have tried:
 
1. Complete uninstall and re-install of both programs independantly.
2. Changing the buffereing stettings.
3. Changing the output prioritys.
4. Changing the windows program priorties.
5. Running in windows compatibility mode.
6. Changing everything and hope for the best.
7. Re-editing and saving virgin MIDI file (what a nightmare).
 
So far nothing has sorted the problem.
 
I use a Toshiba Satalite laptop (Vista) and a Roland JV 1080 to create the sounds through the PA system. When editing at home I just use the onboard windows soundcard do the job.
 
I had thought that as the laptop has got older and slower it might need a boost of RAM to help out? The laptop runs Vista home edition but had no trouble in the past so it must be compatible.
 
If you have taken the trouble to read this and know how to help, please, please, please get in touch and I will be forever in your debt.
 
Roger Coates
Yorkshire
UK