Akai S1000 / S1100 samplers

Hi, I have just recently acquired an Akai S1000 sampler, and am 
buying another one, but have hit upon a technical problem / glitch 
with using it.
 
I have experienced this problem with both the operating system which 
came pre-installed on the ROMS of the unit (v2.00), and have since 
tried downloading the latest operating system v4.40 from Akai's 
website, but still the problem remains.
 
This is the sequence of events (I have tried several times in case 
the 'fault' was a one off)
 
After I have made several stereo samples (using MIDI note as a 
trigger rather than threshold in case this is relevant), and assigned 
them to programs and keygroups, and individual midi channels, when I 
trigger them one by one from a midi keyboard, one or two of the 
stereo samples only plays the -L, or -R part of the sample 
intermittantly, ie this fault fluctuates as I keep pressing the midi 
key that triggers it, the fault occurs and doesn't occur - randomly 
fluctuating.
 
I have set Coherance to be on for all samples, but the problem 
remains.
 
Apart from this, the sampler is an excellent machine, but I need to 
remedy this as it will cause Stereo inconsistancy in my compositions.
 
Is this a known technical issue with the machine, or do I need to 
have it repaired?
 
Many thanks for your time as I cannot find any info out there, and 
I'm going nuts trying to remedy it!!!