Is working just fine for me. Can not get it to fail with 32 and 64 bit IDE. buffering 6088 line features.
>>> import arcpy
>>> arcpy.env.overwriteOutput = True
>>> listTable1 = "\\\\mcflight01\\MCFlightData\\HGIS\\Data\\WCH.gdb\\WasteSites\WasteSitesLine"
>>> distances = [100,300]
>>> bufferunit = "Feet"
>>> arcpy.MultipleRingBuffer_analysis(listTable1,"C:/Users/rkzufelt/Documents/ArcGIS/Default.gdb/WasteSitesLine_MultipleRingB",distances,bufferunit,"distance","NONE")
<Result 'C:\\Users\\rkzufelt\\Documents\\ArcGIS\\Default.gdb\\WasteSitesLine_MultipleRingB'>
>>>
I can not get it to work the way you have your distances in Also, if I try to set distances[0]= anything, I get list assignment index out of range error unless you have already assigned the list objects for the two index positions, in which case, no need to re-set them. The only snippet of your code that I can get python to accept without error is the bufferUnit= "feet".code example:
distances[0] = 100
distances[1] = 300
bufferUnit = "feet"
arcpy.MultipleRingBuffer_analysis(inFeatures, outFeatureClass, distances, bufferUnit,"","NONE")
Take a look at my code, and see if that works for you (substituting your data of course),R_If still not working, other posts about this issue have had "corrupt" data sets. Once they cleaned them up, the errors went away. Might try on a smaller, "clean" data set and see if you can get it working.