Error using trainCasca​deObjectDe​tector function

Hello ,

i get the follwoing error when trying to use trainCascadeObjectDetector function

Error using trainCascadeObjectDetector>getTotalNumInstances (line 684)
imageFilename field for image number 1 must be a non-empty char vector

Error in trainCascadeObjectDetector>populateTrainCascadeParams (line 368)
totalPosInstances = getTotalNumInstances(filenameParams.positiveInstances);

Error in trainCascadeObjectDetector (line 177)
    featureParams, totalPosInstances] = populateTrainCascadeParams(parser);

Error in myCascadeObjectDetector (line 19)
trainCascadeObjectDetector('oneDetector.xml',positiveInstances, negativeFolder,'FalseAlarmRate',0.1,'NumCascadeStages',5);

How to overcome this problem?

Best Regards

Hossam Alzomor