To Export a model using command prompt:

1. Open command prompt as run as administrator

2. change the directory to management utilities 

for ex: if the managementUtilities are present in E:\Program Files\Microsoft Dynamics AX\60\ManagementUtilities

3. change directory to E drive using cd E:

4. once the directory is changed enter the command E:> E:\Program Files\Microsoft Dynamics AX\60\ManagementUtilities

5. E:\Program Files\Microsoft Dynamics AX\60\ManagementUtilities> axutil export /model:DES /file:BPCheck (where DES is the existing model and BPCheck is the filename we need to export) 

Finally the model will be exported to E:\Program Files\Microsoft Dynamics AX\60\ManagementUtilities.