Hmmm. Out of over 1200 images, only 26 are less than 300 wide and 57 are less than 300 high. A total of 11 are 300 or less in both dimensions.
 
However, considering the possibility that the size may be a factor we'll start tracking which ones we have issues with. File size can't be an issue - the largest is 12K...

make a backup copy of your images.
convert all of them to less than or equal to  300 x 300
 
Xnview is free and you can do it in batch mode so its painless
 
run some boms
 
ahh ! much better

sounds like we need a vector format for thumbs if your using line drawings.
 
anyway to update the cad to thumbs you might use wintask. (http://www.wintask.com)
 
use something like this  (run it in a dos box in the root directory of your drawing files.)
 
dir *.iam /b/s/d > c:\iam.txt
 
to make a list of all the drawing files  (file names will be in the file created on your C drive. iam.txt in this case)
 
Get that in excel and feed it to a wintask script that drives the cad program to redo all the thumbnails.
 
here's an example of a wintask script
you simply record these like a word macro.
I added the program lines the loop thru this.
 
it basically copies the file name with path from excel
uses that to open the file in the cad program
then uses the cad program to make the thumbnail
returns back to excel
marks the file name as processed by changing the color of the cell and moves down to the next file name.
 
then it loops
 
I've used this technique to do some big jobs in DBA and other programs that would have taken weeks or months manually.
 
from my experience:
use dba classic for this   I didn't have much luck with evo
 
use keyboard commands where ever you can. I find it works better/faster than mouse clicks.
 
sometimes these scripts will stall so you have to restart them. Still its way easier to babysit a script than to do the work manually.
 
I usually run them on an unused PC using gotomypc so I can run them in a window and use my PC for other things while the script is doing its magic.
 
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
'example wintask script.
 
a = 0
pause 10 ticks
Repeat
#SendKeysDelay = 10
 
 
 
UseWindow("EXCEL.EXE|EXCEL7|pfiptlist",1)
     SendKeys("<Ctrl c><Alt>")
 
UseWindow("INVENTOR.EXE|MDIClient|Autodesk Inventor 11|1",1)
     SendKeys("<Alt f>")
 
'UseWindow("INVENTOR.EXE|Afx:00400000:8:00010011:00000000:06DD04CD|Autodesk Inventor 11",1)
     ChooseMenu(Context,"&Open...")
 
'UseWindow("INVENTOR.EXE|Edit|Open|1",1)
     SendKeys("<Shift <Ins>><Enter>")
 
'UseWindow("EXCEL.EXE|EXCEL7|",1)
'UseWindow("INVENTOR.EXE|#32770|Open",1)
'      Click(Button,"&Open")
'-=-=-=-=-=-=
'zoom all and turn off work planes
 
           SendKeys("<Alt v>")
 
'UseWindow("INVENTOR.EXE|Afx:00400000:8:00010011:00000000:06DD04CD|Autodesk Inventor 11 - []",1)
     ChooseMenu(Context,"O&bject Visibility|All Workfeatures")
 
UseWindow("INVENTOR.EXE|AfxFrameOrView70u||1",1)
     SendKeys("<F6>")
 
     '-=-=-=-=-=-=-=-=-=-=-
 
UseWindow("INVENTOR.EXE|AfxFrameOrView70u||1",1)
     SendKeys("<Alt f>")
 
'UseWindow("INVENTOR.EXE|Afx:00400000:8:00010011:00000000:06DD04CD|Autodesk Inventor 11",1)
'UseWindow("INVENTOR.EXE|Afx:00400000:8:00010011:00000000:06DD04CD|Autodesk Inventor 11 - [PFBVK00001]",1)
     ChooseMenu(Context,"Save Copy &As...")
 
UseWindow("INVENTOR.EXE|Edit|Save Copy As|1",1)
     SendKeys("<Home>k:\thumbspc\<Tab>")
 
UseWindow("INVENTOR.EXE|#32770|Save Copy As",1)
     ChooseItem(Combo, "4", "PNG (*.png)", single, left )
     Click(Button,"&Save")
 
UseWindow("INVENTOR.EXE|AfxFrameOrView70u||1",1)
     SendKeys("<Alt f>")
 
'UseWindow("INVENTOR.EXE|Afx:00400000:8:00010011:00000000:06DD04CD|Autodesk Inventor 11 - [PFBVK00001]",1)
'UseWindow("INVENTOR.EXE|Afx:00400000:8:00010011:00000000:06DD04CD|Autodesk Inventor 11 - []",1)
'UseWindow("INVENTOR.EXE|Afx:00400000:8:00010011:00000000:06DD04CD|Autodesk Inventor 11",1)
 
     ChooseMenu(Context,"&Close")
 
'-=-=-=-=-=-=-=
'say no to close save changes
 
UseWindow("INVENTOR.EXE|#32770|Autodesk Inventor 11",1)
     Click(Button,"&No")
 
'-=-=-=-=-=-
 
UseWindow("INVENTOR.EXE|MDIClient|Autodesk Inventor 11|1",1)
     SendKeys("<Alt>")
 
UseWindow("EXCEL.EXE|MsoCommandBar|Formatting",1)
     ClickMouse(Left,Down,575,10)
     ClickMouse(Left,Up,575,10)
 
UseWindow("EXCEL.EXE|EXCEL7|pfiptlist",1)
     SendKeys("<Down>")
 
 
 
 
 
pause 10 ticks
 a = a + 1
 
Until a = 200
 
 

We print drawings from word documents.
I do a copy link from Autocad and paste that into word,
and the word doc is printed with the traveler.
sometimes we need a large format drawing (size D or E) for a machine assembly.
these I print manually on the plotter although one of my guys sends the word docs to the plotter and they do print out fine large format even though at 8.5 x 11 you can barely read the words.
The vector format scales cleanly.
 
if you can save or convert your cad files to .WMF  thats a vector format and may work well for your situation. Autocad can do wmf. I never used one in dba though
 
it is listed as a supported format for thumbs.
 
 
 

I just tried a WMF (vector format) for a cad drawing of a circuit board and printed it about 1/4 inch square
when I zoomed in it looked quite good.
 
I may use this for some of my items.
 
 
 

It's always something.
 
There are DWG and DFX to WMF converters.
 

is it larger than 300 x 300 ?

Try reducing the bit depth of the image. try 8 or 16 bits. or black and white.
 
I find EVO has issues with complex shaded images and its worse as they get larger.
I've change logo images and has some the black out 100 % of the time. When I made them smaller and less bit depth and it fixed the issue (mostly).
 
there seem to be something that builds up. Maybe a memory leak in the printer driver or a buffer that overflows on itself.