I know it's not what you want to hear, but the problem is on your end. It was very common for people to get image errors when using the DM patch. The standard advice is to start from scratch because you probably installed the patch wrong.
Only other possibility I can think of is an issue with one of the archives. What version of the main game did you download? I have the official light compressed archive, named "EcchiSensei-Week_1-light_compressed.zip". The SHA-256 checksum* is
4C788499131FD5696C0A59278DB09B7FE9C27AB4200465313641EB603AB6B17D
The SHA-256 checksum of the DM patch archive I have (named "EcchiSensei-Week_1_DMpatch.zip") is
F132A42E36B9127879A0FBCC282348A00031E0E0B47F4A0EB0F58993CB1FEDE4
I get a warning (Headers error) when extracting the DM patch with 7-zip but it is not something to worry about.
* If you have a recent version of 7-zip installed, you can calculate the checksum like this:
View attachment 1884270
I recommend
this fix by
TanusMorken.
Note, it may cause an error the first time you start the game with it. Did for me anyway. Just quit and re-launch.