OK, I have a Time Capsule that works perfectly and an EPSON RX680 that works perfectly. But When I try to make my printer/scanner wireless by plugging it into my Time Capsule, all hell breaks loose, nothing works, and I am referred in an endless loop between different troubleshooting assistants and config menus. 
All I want to do is scan something through Photoshop.
I choose File > Import > EPSON RX680/RX685/RX690...
Then comes the error:
Epson Scan cannot be started.
There may be a problem with the network settings. Please use the Troubleshooting Assistant to solve the problem. Do you want to open the Troubleshooting Assistant?
I of course click "Yes".
The assistant opens (it's just a bunch of HTML pages listing generic problems). Meanwhile Photoshop alerts me that it "Could not complete the Import command because there is no scanner installed."
Fantastic. Well it is installed, just not recognized when trying to go through the Time Capsule.
So I go to SysPrefs and look at my printer settings. My printer/scanner is showing up and is listed as "idle". The "Share this printer" box is checked. It's being recognized over the wireless network after all, so what gives?!
I go to my Utilities folder and open EPSON Scan Settings.app
This utility is utterly useless. There is a radio button to select either Local or Network. Of course I choose Network. I click the "Add" button to add my printer since none are listed. I assign it a name and type in my IP address (yes, type... the utility doesn't allow copy/paste). At least I think this is my IP address, since I Googled "what's my IP?" and this is what I found. The utility confirms the IP is valid. Yay.
So I click the "Test" button and of course it fails:
The connection test has failed.
Please use the Troubleshooting Assistant to solve the problem.
Do you want to open the Troubleshooting Assistant?
Does this look familiar???
Just going in circles at this point.
I find a support page on Apple.com:
http://support.apple.com/kb/TS1253
I follow the steps.
I open Airport Utility.
I see my Time Capsule.
I click "Manual Setup"
I click the Printers tab.
I check "Share printers over Ethernet WAN port."
I check "Advertise printers globally using Bonjour". (not sure if this is necessary or relevant)
I then go back to the Airport tab and within that I select the Time Capsule tab and click the "Edit" button. I check "Use dynamic global hostname" (I have no idea what I'm doing now)
I assign a hostname, username, and password.
I check "Allow configuration over Ethernet WAN port" and "Advertise configuration globally using Bonjour" and click Update.
In the next window I am told to "Correct the problem below before updating this Apple wireless device:
Item:
This Apple wireless device is set up to allow configuration over the Ethernet WAN port, which decreases network security."
OK fine... I uncheck the box to "Allow configuration over Ethernet WAN port"... essentially undoing what I just did. Stupid. Pointless.
This is as far as I have been able to get and I am exhausted. Anyone with printer expertise - please help!
All I want to do is scan something through Photoshop.
I choose File > Import > EPSON RX680/RX685/RX690...
Then comes the error:
Epson Scan cannot be started.
There may be a problem with the network settings. Please use the Troubleshooting Assistant to solve the problem. Do you want to open the Troubleshooting Assistant?
I of course click "Yes".
The assistant opens (it's just a bunch of HTML pages listing generic problems). Meanwhile Photoshop alerts me that it "Could not complete the Import command because there is no scanner installed."
Fantastic. Well it is installed, just not recognized when trying to go through the Time Capsule.
So I go to SysPrefs and look at my printer settings. My printer/scanner is showing up and is listed as "idle". The "Share this printer" box is checked. It's being recognized over the wireless network after all, so what gives?!
I go to my Utilities folder and open EPSON Scan Settings.app
This utility is utterly useless. There is a radio button to select either Local or Network. Of course I choose Network. I click the "Add" button to add my printer since none are listed. I assign it a name and type in my IP address (yes, type... the utility doesn't allow copy/paste). At least I think this is my IP address, since I Googled "what's my IP?" and this is what I found. The utility confirms the IP is valid. Yay.
So I click the "Test" button and of course it fails:
The connection test has failed.
Please use the Troubleshooting Assistant to solve the problem.
Do you want to open the Troubleshooting Assistant?
Does this look familiar???
Just going in circles at this point.
I find a support page on Apple.com:
http://support.apple.com/kb/TS1253
I follow the steps.
I open Airport Utility.
I see my Time Capsule.
I click "Manual Setup"
I click the Printers tab.
I check "Share printers over Ethernet WAN port."
I check "Advertise printers globally using Bonjour". (not sure if this is necessary or relevant)
I then go back to the Airport tab and within that I select the Time Capsule tab and click the "Edit" button. I check "Use dynamic global hostname" (I have no idea what I'm doing now)
I assign a hostname, username, and password.
I check "Allow configuration over Ethernet WAN port" and "Advertise configuration globally using Bonjour" and click Update.
In the next window I am told to "Correct the problem below before updating this Apple wireless device:
Item:
This Apple wireless device is set up to allow configuration over the Ethernet WAN port, which decreases network security."
OK fine... I uncheck the box to "Allow configuration over Ethernet WAN port"... essentially undoing what I just did. Stupid. Pointless.
This is as far as I have been able to get and I am exhausted. Anyone with printer expertise - please help!