I tried the solutions listed on the Adobe "Unit type conversion error" support page but nothing seems to help. Here is the error log:
/Users/[username]/Dropbox/Productivity-tools/Alfred.alfredpreferences/workflows/user.workflow.8C375D70-662E-4FC5-8FD8-9BD0F84E547F/browser_tabs/applescript_utils.rb:30:in `block in osascript': AppleScript error: 2014-05-26 21:35:32.757 osascript[741:507] Error loading /Library/ScriptingAdditions/QXPScriptingAdditions.osax/Contents/MacOS/QXPScriptingAdditions: dlopen(/Library/ScriptingAdditions/QXPScriptingAdditions.osax/Contents/MacOS/QXPScriptingAdditions, 262): no suitable image found. Did find: (BrowserTabs::AppleScriptUtils::AppleScriptError)
/Library/ScriptingAdditions/QXPScriptingAdditions.osax/Contents/MacOS/QXPScriptingAdditions: mach-o, but wrong architecture
osascript: OpenScripting.framework - scripting addition "/Library/ScriptingAdditions/QXPScriptingAdditions.osax" declares no loadable handlers.
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/open3.rb:217:in `popen_run'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/open3.rb:99:in `popen3'
from /Users/gravicle/Dropbox/Productivity-tools/Alfred.alfredpreferences/workflows/user.workflow.8C375D70-662E-4FC5-8FD8-9BD0F84E547F/browser_tabs/applescript_utils.rb:25:in `osascript'
from /Users/gravicle/Dropbox/Productivity-tools/Alfred.alfredpreferences/workflows/user.workflow.8C375D70-662E-4FC5-8FD8-9BD0F84E547F/browser_tabs/applescript_utils.rb:11:in `run'
from /Users/gravicle/Dropbox/Productivity-tools/Alfred.alfredpreferences/workflows/user.workflow.8C375D70-662E-4FC5-8FD8-9BD0F84E547F/browser_tabs/commands/command.rb:42:in `run'
from /Users/gravicle/Dropbox/Productivity-tools/Alfred.alfredpreferences/workflows/user.workflow.8C375D70-662E-4FC5-8FD8-9BD0F84E547F/browser_tabs.rb:51:in `run_command'
from /Users/gravicle/Dropbox/Productivity-tools/Alfred.alfredpreferences/workflows/user.workflow.8C375D70-662E-4FC5-8FD8-9BD0F84E547F/browser_tabs.rb:24:in `tabs'
from filter.rb:7:in `<main>'