I can't generate PDF file

I have never seen anyone report that failure message.

I wonder if it it is the right version of Java. See https://www.grainge.org/RoboHelp_Tour/rh2022/outputs/outputs_pdf.htm. Test by opening the About RoboHelp sample project and see if you get the same message.

• If you do, then maybe it is your java version. Otherwiose I suggest for this one you need to go to Adobe Support. See https://helpx.adobe.com/contact/enterprise-support.other.html#robohelp for your Adobe Support options. The email link tcssup@adobe.com is recommended as it reaches a team dedicated to Technical Communication Suite products including RoboHelp.
• If you do not, then it suggests something in the content is causing the issue. Try Divide and Conquer as described below.

Zip up the project so you have a copy that cannot accidentally be opened and worked on. That gives you a copy that you can safely revert to later if needed. Save the zip file somewhere safe.

METHOD ONE

1. In the new UI the output is controlled by what is in the TOC so create two copies of your TOC and delete different halves of the content from each. One should work and one should fail. 
2. Assuming one half only failed, create a copy of it and again delete different halves. By repeating that you should narrow things down to the topic(s) that are giving grief.
3. If both failed, you need to create smaller and smaller sections.

METHOD TWO

1. Create a new TOC and drag to it the first folder in the Contents panel.
2. Generate that and if it works, drag the next folder.
3. When generating fails, delete all other folders from the TOC and then create two copies of the TOC.
4. Delete different halves of the content from each.
5. Generate again and one should work and one should fail. Repeat until you track down the rogue topic(s).

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My site www.grainge.org includes many free Authoring and RoboHelp resources that may be of help.