EDIT: Wait a minute. I just re-read your question. An .ashx file, such as a .asmx or .aspx file, is a markup file, not a code file. You cannot use regions in these files. You can only use regions in the code behind the files associated with them (for example, .ashx.cs files).
Original answer: As a rule, whenever I get such inexplicable odd behavior in VS2010, I reset all settings that usually fix the problem.
Try tools-> Import and Export Settings → Reset All Settings and check if this fixes the problem in your area.
If not, this could be due to a bad add-in or extension. Try disabling extensions / add-ins to make sure this fixes your problem, try starting in safe mode and see if the IDE leads:
DEVENV.EXE /safemode
Hope this helps.
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