Here are some links to various resources regarding QB PDF Converter, and problems emailing from QB. If the QB PDF Converter has a problem you will also not be able to email from QB. Some 64 bit computers will have trouble with emailing from QB, whereas other seemingly the same 64 bit computers will not have the issue.
If on QB version 10 and prior version update to the latest R number release. Try QB PDF or email again. If not successful repair the QB PDF converter with the link below. If all else fails update to version 11 of QB. Unfortunately upgrading will be much faster than spending hours troubleshooting this issue. In most cases on v10 and prior you will not be able to fix the issue.
Link to uninstall and reinstall the QB PDF converter. Normally the best thing to do is run the PDF fix and skip this step entirely.
Use the below link to troubleshoot QB PDF converter and emailing issues.
Direct link to PDF fix; QB PDF Diagnostic Tool.