Looks like the value you used is outside the range for float:

http://technet.microsoft.com/en-us/library/ms173773.aspx

- 1.79E+308 to -2.23E-308, 0 and 2.23E-308 to 1.79E+308

>I have this command:
>
>

>DECLARE @ModUser Int
>DECLARE @ModDate DateTime
>DECLARE @AvailableDiskSpace BigInt
>DECLARE @TotalDiskSpace BigInt
>DECLARE @AvailableDiskSpacePercent Float
>DECLARE @Numero Int
>
>SET @ModUser=1
>SET @ModDate='2014-02-23 18:24:58'
>SET @AvailableDiskSpace=4.34447218344401E-313
>SET @TotalDiskSpace=6.29967500442815E-313
>SET @AvailableDiskSpacePercent=68.963433516653
>SET @Numero=16
>
>UPDATE Storage
> SET ModUser=@ModUser,ModDate=@ModDate,AvailableDiskSpace=@AvailableDiskSpace,TotalDiskSpace=@TotalDiskSpace,
> AvailableDiskSpacePercent=@AvailableDiskSpacePercent
> WHERE Numero=@Numero
>

>
>I receive this:
>
>Warning: the floating point value '4.34447218344401E-313' is too small. It will be interpreted as 0.
>Warning: the floating point value '6.29967500442815E-313' is too small. It will be interpreted as 0.
>
>It is not clear what has to be adjusted.