Did you ever find a solution for this issue?
I am having the exact same issue with an HP EliteBook Folio 9480m. On 45+ other models I support, the Package I am calling from a Task in my TS executes successfully. However, on the HP EliteBook Folio 9480M, it fails. The Task runs a CMD-Line (Name.HTA) ... that's it ... it just calls an HTA.
I suspect it may have something to do with the WinPE 3.0 x86 Mass Storage Driver, but I am not sure.
Update (2014-11-19):
The 9480M has a C:\ drive, but there is no C:\_SMSTaskSequence folder ... therefore, the Packages cannot copy the source files locally. My TS errs-out with a 0x800700A1 error. I have tried updating my BOOT.wim with a more recent version of the iaStorAC.inf (Intel® Desktop/Workstation/Server Express Chipset SATA RAID Controller), but that has proven not to be successful.
Guess I am still looking for the correct Mass Storage Driver for WinPE 3.0 x86.