If you logon to a windows client or switch to a different user you are getting an error message.
It doesn't seem to have any other implications, you can work normally with Lotus Notes.
Dos windows pop-up error message :
Error writing to process file pid.nbf, (other applications may be inappropriately accessing this file)
On a Windows 7 (64bit) test client it was sufficient to give the group users write permissions on the Lotus Notes installation folder C:\Program Files (x86)\IBM….
In the environment of one customer this didn’t resolve the issue but giving the group everyone write permission on that folder solved the problem.
Confirmed on Windows 7 (64bit) and Windows XP
SEP 11.0.5 - 11.0.6 MP2
Lotus Notes 8.5.x