cost is NaN

[chirstinaFan]

Epoch 1 Update 510 Cost 308.02814 UD 0.764338970184
Seen 60000 samples
Epoch 2
Epoch 2 Update 520 Cost 118.96719 UD 0.695561885834
Epoch 2 Update 530 Cost 226.9092 UD 0.454373121262
Epoch 2 Update 540 Cost 11.716671 UD 0.462770938873
Epoch 2 Update 550 Cost 25.91058 UD 0.57851600647
NaN detected

can you meet this problem?