Why can't I successfully upload multiple split 7z files?

[Anita Chen]

My Confluence has Attachment Checker for Confluence enabled to restrict file formats for uploading.
The settings are as follows: MPG, MOD, WMV, 3G2, OGV, MPEG, RMVB, RM, VOD, OGA, MP3, FLV, MOV, FLV, MP4, OGG, AVO, 3GP, MKV, DAT.

I have split the file using 7z into xxx.7z.001 and xxx.7z.002. I am able to successfully upload xxx.7z.001, but I cannot upload xxx.7z.002.