Cannot unzip ucf101_jpegs_256.zip

[Nicky66667]

I followed the 1.3 section to download the RGB images.

After I downloaded the data from links, and generated ucf101_jpegs_256.zip by this command: cat ucf101_jpegs_256.zip* > ucf101_jpegs_256.zip.

However, an error happened when I tried to unzip it.

Here is the error message:
Archive: ucf101_jpegs_256.zip End-of-central-directory signature not found. Either this file is not a zipfile, or it constitutes one disk of a multi-part archive. In the latter case the central directory and zipfile comment will be found on the last disk(s) of this archive. unzip: cannot find zipfile directory in one of ucf101_jpegs_256.zip or ucf101_jpegs_256.zip.zip, and cannot find ucf101_jpegs_256.zip.ZIP, period.

What caused this error, and what should I do?