Excessive delay in opening 'Create Video File' option list

[Bruce S]

After normal trimming and deleting various video clips (and adding transitions) in the 'editing phase' of my new project using Version X6, there is a problem when when moving to 'Share/Create Video File'. After clicking the 'Create Video File', there is a delay of about 6 seconds before a blank, black drop-down box appears. The black box (with no white selection options) stays for a further 60 seconds before a brief flash of the options list and then the box disappears. This same effect can be replicated after many attempts (no further changes to any editing) but very occasionally, the selection list will hold in place and normal rendering can be managed OK. If a separate project is created with the same video files but with no editing (trimming or deleting), there is no problem with the 'Create Video File' activation. Note that no music or titles have been added at this stage.
This is my first attempt to edit large HD files from my Sony HDR-PJ760 camera. I am using about 250 files (total size approx. 17.4GB). When I have managed to get stability on the 'Create Video File' option list, rendering of this initial trial editing phase took approx. 80 minutes which seem OK for the size of the files.

No external devices are being used during the editing or rendering phase.

Using Video Studio Pro (X6) - 16.1.0.45 - including latest service pack update.

Source Files from Hard Drive (C:) - file format (PAL HDMV), Video Type(H.264 Video), [24bits,1920X1080, 16:9, 50fps], Audio (Dolby Digital)

Files were initially obtained on Sony HDR-PJ760 Camera (on camera hard drive) and transferred to computer (C:) via USB.

Camera file type- AVCHD Video (.MTS)

Video data rate - 26186 kbps, Total bit rate - 26442kbps, Frame rate - 50 frames per sec. Audio -Dolby Digital Audio 448kbps.

Project Properties - File size - 603.5kb, Duration - 37.55 min, Edit file format - Microsoft AVI files, 24 bits, 1024X576, 50 fps, Uncompressed PCM, 44.1000kHz,,16 bit stereo.

The only problem seems to occur at the SHARE/Create Video File dropdown menu. No ERROR CODES have appeared.

Would greatly appreciate any thoughts on this problem. Many thanks. Bruce S