Error: The provided entity lists contained only generic or high-frequency words. Please provide additional unique entity names for training

I was trying to train Comprehend to identify my custom types. When I submit a training job to identify my custom entities it comes up with the error below.

"The provided entity lists contained only generic or high-frequency words. Please provide additional unique entity names for training."

What does the error really mean?

I had created 5 entity type each having 200 different text and then nearly 40 documents of training data. Each of the training data were store as separate files in the s3 bucket. I provided spearate S3 bucket names for both the entity.csv and for the 40 documents stored as txt files

Any help will be appreciated