There is really not enough information here to even provide an educated guess on the Cause fo thsi problem, but, after looking at some lab case, here si what I found:
When the customer selects the session id from the restore, The following message is displayed in a pop-up on DP GUI.
[12:1007] Unknown Internal error
# While browsing restore chain for an object, if an enhanced
# incremental backup's corresponding full backup has already
# expired, then Database Session Manager displays internal error.
# If this variable is set to 1, it will disable popup "Unknown Internal Error".
In the 'global' file, find this line
# IgnoreMissingFullWhileRestore=0 or 1
# default: 0
Make a copy of this line, remove the # sign and the 'space' that follows, and set it to '1'
IgnoreMissingFullWhileRestore=1
# IgnoreMissingFullWhileRestore=0 or 1
Save the file, stop and restart DP
=================
[query_LISTDIR][entry] directory='/arch', view=-1
[ 80]
[dcbrowse_list_dir][entry] directory="/arch", view=-1, flags=0
[ 5] 2012-04-18 11:57:49 ("/db/dc/dcbrowse/dcbrowse.c $Rev: 25204 $ $Date:: 2011-10-14 15:43:07":3717) A.06.20 bDPLNX_00169(b621)
[ 5] [MARK 3] in dcbrowse_list_dir
Code is:1007
This was fixed with the 6.20 patch bundle
If neither of these seem to correspond to your issue, open a case with the response center
