You may be confused by the error in Excel saying
¿another user¿. Actually Excel cannot tell who
(the real human) is editing the file. Based on my
research the No.1 possibility of the error is
KB2626998.
2626998  Connection to a network document is lost
in the 2007 Office system or in Office 2010 after
the computer resumes from standby
http://support.microsoft.com/kb/2626998

For Excel 2010, follow these steps:
a.  Click Start , click Run , type regedit in the
Open box, and then click OK .
b.  Locate and then select the following registry
subkey:
HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Excel\Options
c.  On the Edit menu, point to New , and then
click Dword Value .
d.  Type NetworkAvailableTimeInSeconds , and then
press Enter.
e.  Right-click NetworkAvailableTimeInSeconds ,
and then click Modify .
f.  In the Value data box, click Decimal , type a
number value, and then click OK .

Note This registry subkey sets the time, in
seconds, that Excel waits for the network to
resume. For example, if you type 15 for the number
value, Excel waits 15 seconds for the network to
resume. You might have to do some tests in your
own environment to determine an appropriate value.
You may have to try multiple numbers.
g.  Locate and then select the following registry
subkey.
HKEY_CURRENT_USER\Software\Microsoft\office\14.0\common\Internet
h.  Repeat step 2C through step 2F again. Reuse
the same value that you used previously.
i.  Exit Registry Editor. 

DONE

Task reassigned to Ranjit Kayastha.