I tried to accepting collaborator invitations and uploading file or folders however I got a following error message.

"Partial upload failed", "There was a problem when uploading. Please try again"

I am unable to upload it, regardless of how many times I tried.

See also “Troubleshooting uploads to Box”, but it didn’t seem to have any factor.

※For example, even just to I tried upload a word file with only 12KB (3 letter filename), will get an error.

Are there any other factors causing such errors? 

Looking forward to hearing from you.

Thank you.