to find Financial Rate in c#

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C#3.0

C#

ASP.NET

i've used Microsoft.VisualBasic.Financial class to find Rate

here is the below code i've used,

lblEffcost.Text = (((Financial.Rate(_RATE_Param1, _RATE_Param2, _RATE_Param3, _RATE_Param4, 0, 0)) * 12) * 100).ToString();

here in above for some parameter the Rate method is working fine, for some other parameters its showing an exception error as

"Cannot calculate rate using the arguments provided"

but for those parameters are working in Excel sheet
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Some how i need to find Rate as like excel....
can some one give idea or any other free dll or api or apk to get Rate