Make sure all harddrives involved (including temp drive) have plenty of space.

You need free space at least double the size of your finished disc.

Also DVDA is a 32 bit programme so limited in the amount of your system memory that it can use. There is a patch available that tries to address this. You will find a link for it in this thread https://www.vegascreativesoftware.info/us/forum/problem-with-burning-blu-ray-discs--148274/#ca932924

Personally I've never had to use it, even when creating an iso of nearly 25gb.

My new problem is when adding media to a .dar file the program works to 43% of opening media files.. and freezes at that point. I have plenty of memory and space in the files designated for the program to work. I'm using Build 100.

my video files are .avc format.

I also get "One or more flie plug-ins necessary for preparing the disc are missing or corrupt. please reinstall the apapplication.... I do that over and over.. same error message.

One thing to try - which may or may not work - is to reset DVDA back to its default (factory) settings using the procedure outlined in: https://www.vegascreativesoftware.info/us/forum/faq-how-can-i-reset-vegas-pro-to-default-settings--104646/

Make sure that you keep Shift+Ctrl depressed while you double-click on DVDA's desktop icon (not the taskbar icon) and then check the checkbox to clear the cache.

After doing what you suggested.. I get the following error pop up when I try to prepare the .iso:

The Main Concept MPEG plug-in was not able to initialize properly. It appers that some modules are bing used from a folder other than the install folder. Most likely another 3rd party application has installed MainConcept modules in the system folder. These may conflict with this plugin. Please contact Sony Customer Support for assistance.

... when adding media to a .dar file the program works to 43% of opening media files

Is that all and any media that you are adding to DVDA - i.e. all fail at 43% ... or just the one media that is failing at 43%? If the latter, perhaps there is some corruption with the media at the 43% point that DVDA spits the dummy on

It appears that some modules are being used from a folder other than the install folder. Most likely another 3rd party application has installed MainConcept modules in the system folder. These may conflict with this plugin.

Are the .avc files rendered from Vegas Pro or from Vegas Movie Studio? If not, could it be possible that the other program being used to render the .avc files has introduced an MC MPEG codec that DVDA doesn't like? Otherwise, are there any other programs on your computer that might have installed an MC MPEG codec that overrides that used by DVDA?

Also, I assume that DVDA is entirely installed on the C drive and not on another drive.