That warning is from my Spreadsheet::Read, which not only issues a warning, but also generates a patch to correct it. As said, the recent Spreadsheet::ParseExcel updates have fixed it already. BUT ...

The new version 0.28 has several problems:
* It is expecting Jcode and Unicode::Map to be installed as prerequisites unconditionally. Just for supporting Japanese.
* It requires IO::Scalar for opening streams, which is not needed for all perl versions that have PerlIO.

I have sent a patch to Gabor to fix both issues, but have no reply yet.
Until then, I would suggest to install Spreadsheet::Read and apply the generated patch.