It may be a bad plugin. Try disabling all the plugins and then restarting LR. To disable the plugins:
1. Do File > Plug-in Manager
2. Select a plugin in the left column.
3. In the right column, scroll to the Status section.
4. If necessary, expand the Status section by clicking on the triangle to the left of "Status".
5. Click Disable.
I have encountered the same issue. The problem with what you are suggesting is that when the "Bad argument #1 to ‘loadstring’ (string expected, got Boolean)" message pops up, you cannot access the "File" menu (or anything else in Lightroom for that matter). You have to Ctrl-Alt-Del to get Task Manager, and then end the Lightroom task. That puts us back in "square 1."
Any other suggestions? This problem prevents me from using any part of Lightroom, including the File menu.
You could try resetting LR's preferences, which stores which plugins are installed: Resetting the lightroom preferences file - updated | Lightroom Forums. If the problem is indeed with a plugin, then resetting the preferences will stop LR from trying to load it.
However, there is a subtlety here: If you had previous versions of LR installed (e.g. LR 5), then if the LR 6 preferences are missing, LR will try to convert the LR 5 preferences. So make sure that you rename or move the preference files for all versions of LR, just in case the problem is with a plugin that was first installed in a previous version.
It appears that the problem had something to do with folders under the Lightroom folder. I went into the Lightroom folder and deleted all folders except the original Lightroom Preview folder. Now I can start up Lightroom without it giving me that pesky message and freezing. Thanks for your efforts. It made me "think outside the box."!
I would like to post this message, on the forum, but I could no longer find and option to "reply."
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Your message got automatically posted on the forum. Glad you resolved the problem.