Odd Happenings With Main User Profile

I just had the weirdest experience. I multi-boot and had gone over to my Windows 7 for a bit and was switching back to my main Vista on C:, the usual logon screen appeared and I entered my password.

It then gave me that screen one gets when first logging in to a new Windows Vista installatain. "Preparing your desktop" then it opened up a sort of shadow of my profile with the generic Vista background and only some of my desktop icons and notification ones.

A balloon appeared saying something about an error occurred and you've been signed into a temporary profile. The balloon disappeared before I could read it all.

This was particularly alarming in that I had just had to reinstall Vista due to having incessant "Windows Explorer is not responding...."- type errors which no amount of repair or System Restoring would alleviate (no infections found). But that's another story.

Anyway, all I have in the Event Viewer/Administrative Events are 4 "User Profile Error" entries:

Reading in order...

Windows was unable to load the registry. This problem is often caused by insufficient memory or insufficient security rights.
DETAIL - The process cannot access the file because it is being used by another process. for C:\Users\Peter\ntuser.dat

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and

Windows cannot load the locally stored profile. Possible causes of this error include insufficient security rights or a corrupt local profile.
DETAIL - The process cannot access the file because it is being used by another process.

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and

Windows has backed up this user profile. Windows will automatically try to use the backup profile the next time this user logs on.

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and finally..

Windows cannot find the local profile and is logging you on with a temporary profile. Changes you make to this profile will be lost when you log off.

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As usual the Event Log Online Help is no help at all.
The only red-flagged events prior to that (which I usually ignore completely) are a "Perflib" reading..

The Open Procedure for service "PNRPsvc" in DLL "C:\Windows\system32\pnrpperf.dll" failed. Performance data for this service will not be available. The first four bytes (DWORD) of the Data section contains the error code.

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and a "SideBySide"...

Activation context generation failed for "C:\Program Files (x86)\Nero\Nero 9\Nero PhotoSnap\PhotoSnapViewer.exe.Manifest".Error in manifest or policy file "" on line . A component version required by the application conflicts with another component version already active. Conflicting components are:. Component 1: C:\Windows\WinSxS\manifests\x86_microsoft.windows.common-controls_6595b64144ccf1df_6.0.6002.18005_none_5cb72f96088b0de0.manifest. Component 2: C:\Windows\WinSxS\manifests\amd64_microsoft.windows.common-controls_6595b64144ccf1df_6.0.6002.18005_none_1509f8bef40ee4da.manifest.

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I have since uninstalled Nero Photosnap as I don't use it.

My user profile is an Administrative level one by the way.

I'm going to repeat switching systems a few times to see if it happens again, but would appreciate any comments from you experts.

Edit: I should add that if I do a proper reboot (rather than ise Neosmart's iReboot) it works OK, but it did happen again when I followed exactly the same steps as before.
I've just discovered to my horror that all my System Restore points have been wiped.

Well, I think you can ignore the above. (Did I hear a loud sigh of relief?)

As things were working prefectly until this morning I used a process of elimination. The only things that had changed since yesterday were, I installed MalwareBytes Free, shouldn't be the cause especially as I hadn't run it yet. I did, however, install the beta Symantec UAC Tool which makes the UAC prompt a little more friendly. Since uninstalling that I haven't had the problem.

Now why that would be the case shall forever remain shrouded in mystery.

I rest my case.