Hello Shubhendu,
I assume with "parameter" you mean a structured parameter with several fields? In that case the symptom you describe is quite common: some field offsets (the byte position inside the structure, where a certain field starts) are calculated incorrectly (e.g. a missing alignment byte or wrong fields lengths of some previous fields) and so the field is truncated.
However, I don't believe that an application that has been using librfc32.dll before, suddenly starts using librfc32u.dll, only because you install it on the server... As I said, in order to replace librfc32.dll with librfc32u.dll, code changes in the application (and consequently a re-compilation) are necessary.
Much more likely the reason is the following: your ASP application already has the correct parameters for communicating with the backend system in Non-Unicode mode. (As the backend has been Non-Unicode so far, this is quite likely.) But up to now there was a very old version of librfc32.dll on that server, that still had bugs in the Non-Unicode communication with a Unicode backend. (I think I remember that some of the older librfc32.dll versions had various problems when communicating with a Unicode backend.) By installing a recent SAPGui version, that buggy librfc32.dll got replaced with a newer version of librfc32.dll, where these bugs are now fixed! The explanation may be as simple as that... 
Best Regards, Ulrich