The conversion is probably being aborted due to the following reasons:

1.The WMV file may be corrupt.
2.The WMV file is protected by Digital Rights Management.

Try using Digital Media Converter's repair utility. This will repair any anomalies present in your file.
To repair your file:
1. On the Tools menu, click Attempt to Repair File...
2. Click Browse to specify the file you want to repair. If a file is selected in the conversion list then that file, by default, is specified as the source file.
3. Click Browse to specify the Destination File. This is the path where the repaired file would be stored.
4. Click Next to repair the file.
5. To add the repaired file to the conversion list make sure that the Add repaired file to the conversion list option is checked.

If the file is digitally protected then it cannot be converted.