NaturallySpeaking 6 has multiple situations where it reports "serious" errors or an "SDAPI" problem.
General procedures to deal with these problems include:
Right-click on "current", select the Rename option, and rename the "current" folder to "old-current".
Right-click on "backup", select the Rename option, and rename the "backup" folder to "current".
Restart Dragon -- this has solved many such problems.
If these steps do not resolve the problem, the next steps I would generally suggest would be an uninstall and reinstall of NaturallySpeaking. But hopefully that step won't be needed often.
Many other errors are resolved with the 6.1 correction, available for Pro/Medical/Legal/Public Safety products.
Several have reported a problem where DNS starts to generate Word documents that have word in ALL CAPS. In general, we have no solution. But a couple of persons have reported that renaming their "normal.dot" Word template file, forcing Word to recreate the file, has solved the problem. Use this with care, as you may have macros or other settings in your normal.dot file.
Otherwise, when this starts to happen, shut down DNS, restart it ... and then order your upgrade to Release 7, which isn't nearly as prone to have this problem.
In e-mail programs, notably Outlook, dictating the word "to" is likely to get you to the "To:" portion of your message. The best solution is to always dictate "to" in context. Second best is installing a "to" command in a dvc file, where the command does nothing except a SendKeys of "to".
This problem, cured with the 6.1 service release, still afflicts Preferred, Standard, and Essentials users. Restarting DNS will temporarily resolve the problem. Changing the attributes of the "tab-key" to be those of a tab key (sounds weird, but that is what you do) can alleviate it. Sometimes it is triggered by tab key statements.