'Potential security issue found in theme'

[Jake Cage]

I'm trying to upload a theme to my forum, when I get this error:

The following errors were encountered:
A potential security issue was found in the theme. It was not imported. Please contact the Author or MyBB Group for support.

I also tried uploading the .xml file to the site, and importing the theme through URL. I got this error:

The following errors were encountered:
MyBB could not find the theme with the file you uploaded. Please check the file is the correct and is not corrupt.

It isn't the calendar.php issue people are familiar with.

I'm running MyBB 1.6.10

[Arbaz]

Which theme are you trying to upload? Also, your attachment is broken.

[.m.]

for potential security issues see replies here (posts #3, #5)

if theme could not be found then check if regular attachments with the posts are working

[Jake Cage]

Worked. Thanks. It wasn't working because I only fixed one of them.