Vista - Access to files as an administrator

I am editing videofilm with Pinnacle studio 11 ultimate with
Windows Vista home premium.
No problems here - until I restart the task and try to
continue my work.
In the act of trying to fetch the recently file, I get the
message that I do not have any access to the file in question
and that I have to ask the administrator about it.
The thing is that /I am/ the administrator and ought to have
full access to everything.

The help menu in Vista recommends me to log on as a standard
user. Then I just have to insert the administrator's password
when I am dealing with files which only the administrator has
access to.

I do so by making another "standard user" which is myself,
using a new name, new password etc. But when I try to open the
file, I am not able to insert any password as it just tells me
that I have no access to the file en question.

So to rephrase:

1. I have logged on as an administrator with full access to
everything in Windows Vista home premium
2. I am thereafter trying to get a certain file from the
computer
3. I am denied this access as a pop-up menu tells me that I am
not entitled to have access to the file and I must get
permission from the administrator, which is - of course
myself.
4. the help menu suggests that I log on as a common user and
when I want to have any access to the files I will be prompted
for the administrator's password
5. I follow this advice, but I am still denied any access to
the file and there is no pop-up box giving me the possibility
to insert the password in question

What do I have to do?

Arne H. Wilstrup
Denmark