Errors converting xcarchive to IPA - single-bundle archive + missing plist method values

I'm trying to convert my xcarchive to an IPA (XCode 7.1.1). The following command

xcodebuild 
    -exportArchive -archivePath foo.xcarchive -exportPath . -exportFormat IPA

Fails with the error

the archive at path 'foo.xcarchive' is not a single-bundle archive

Since the above command is technically deprecated, I also tried the new form:

xcodebuild 
    -exportArchive -archivePath foo.xcarchive -exportPath . 
    -exportOptionsPlist ipa.plist

Where the ipa.plist is as follows:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>method</key>
    <string>app-store</string>
</dict>
</plist>

Which then resulted in the error:

error: exportArchive: exportOptionsPlist error for key 'method': expected one of {}, but found app-store

Now, trying to debug this I opened the xcarchive folder and inspected its structure. I noticed that I have a folder on the same level as Products\Applications\foo.app so I deleted it and tried again to no avail (same results). I then proceeded to delete files from within foo.app until I remained with nothing but the DWARF binary - still no cigar (same result), though that could have been due to the fact that I messed up the app signature by deleting files manually.

Solution

The problem was that one of our post-build steps left a stray folder in the TARGET_BUILD_DIR. This caused the generated xcarchive to be formatted as the dreaded generic archive. My attempts to delete the folder after the fact from the xcarchive itself were doomed to fail since the xcarchive has been flagged generic at the moment of its creation (as evidenced by some missing Info.plist fields). Once I made sure TARGET_BUILD_DIR contained only the .app after all the build phases were said and done, the generated xcarchive was formatted properly as an iOS app archive. That xcarchive, in turn, was easily exported to a proper IPA via xcodebuild -exportArchive -exportPlistOptions, which is the officially supported Apple recommendation that takes care of all the problematic SWIFT support folders and the like.