Perhaps the problem is just that your upper pixel line (which marks where characters are) ends with "white" and ends not with a last "black" pixel?
Unfortunately not. 
I tried it to make black to end, after I made black to the front. The result is same.
After that, I tried to an imported texture (but I made a new folder with new file name) with same character order, but Content Tool just writted the error message.
In last Sunday everything worked well...
I have got same problem. I tried to import a texture with Balzska's method, and with Marcel's method, but the result was same. Content Tool wrote same message which you can see in the post... :/
It is possible to add a option, where we players can disable this CT's option?
It doesn't work for me either the bitmap importer tool. The Content Tool write those message to.
It doesn't work for me neither. I have the same error message. 
Same issue
This is not a LOTUS Logfile and is therefore irrelevant
OK, then it would be interesting, if you can use all of the characters in LOTUS? Even the cross at the end?
Ah, finally I found the problem. The next patch will fix it! 
