One other note... Since in the prior years there was another participant, I assume you were electronically filing the 5500.
For one of the plan we have, the 5500 was electronically filed while there was the other participant. When the other participant terminated and we only had the owner/spouse, we continued to file the 5500 electronically, but with the "one-participant plan" box checked.... which essentially makes the 5500 an EZ (many 5500 questions are not required, and the 5500 is not on the public efast website).
We did this since we thought that if we stopped electronic filing, a flag would be raised somewhere that the 5500 was not filed (or timely filed), even if the EZ was filed directly with the IRS, and we might have to spend time getting this straightened out. We haven't had a problem with this yet.