Ta, Ill try that.
There were 179 historical files in my
H:\\My Documents\\SQL Server Management Studio\\Backup Files\\Solution1
directory of which 99 were non zero in size.
Not sure how many of those SQL Prompt was trying to open however.
This was a comedy of circumstances that lead to such a high number of files, so I don't expect this situation to arise again. Usually I only have about 20 or so open.
An upper limit, or even a prompt window on opening, to allow the user highlight those files to open might be useful if a threshold is breached.