prediction error in ROCR package when sampled y consists of only one class

Dear R users,

Hi. I am using prediction function in ROCR package.
y consists of two classes 0 and 1.
However, since I am using cross-validation, a sampled small number of
y may consist of only one class

y

[1] 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
In this case, prediction function gives an error:
Error in prediction(predic, y) : Number of classes is not equal to 2.
ROCR currently supports only evaluation of binary classification tasks.

How can I solve this problem?

Thank you,
Soyeon Kim