Script Logic : Time Difference

Hello Experts

I am trying to write a script logic to calculate the difference
between two time periods.

Eg:

2012. Feb = 10

2012. Jan = 5

Value = 10-5= 5

I use the following script logic.

*XDIM_MEMBERSET ENTITY = %ENTITY_SET%

*XDIM_MEMBERSET CATEGORY = %CATEGORY_SET%

*XDIM_MEMBERSET ACCOUNT = BS121, BS122

*XDIM_MEMBERSET TIME = %TIME_SET%

*XDIM_MEMBERSET FLOW = 999

*XDIM_MEMBERSET SCOPE = S_None

*XDIM_MEMBERSET RPTCURRENCY = LC

*WHEN_REF_DATA=MASTER_DATA

*WHEN ACCOUNT

*IS BS121

*REC(EXPRESSION = (TIME.TMVL(0,%TIME_SET%)-TIME.TMVL(-1,%TIME_SET%)),ACCOUNT =
CF121,TIME = TMVL(0,%TIME_SET%))

*ENDWHEN

*COMMIT

When I validate, getting following error

Unknown Dimension Name in Keyword: "-TIME. 2013.03 ):,

How can I fix this error.

Your advice much appreciated

Thanks