Once, when the Alter Rebbe was the ba'al koreh, he read a verse slightly incorrectly. Instead of reading 1775 he read 5775. He did so several times and was corrected each time. This was in Parshas Pekudei 38:28, which mentions the sum of 1775 talents collected. ואת האלף ושבע המאות וחמשה ושבעים Instead of reading the "hei" of "ha-elef" (the thousand) with a "patach", he read it with a "tzeirei" (which turns the letter "hei" into 5).
When the 4th time occurred, he walked away and someone else finished the reading. When subsequently asked by the Mitteler Rebbe as to why and what had happened, he responded that at the time he saw a vision that Moshiach would come in 5775. He couldn't read it any other way.
This seems to have been reported by the Mitteler Rebbe even in his Sefer Imrei Bina (some say it was edited and then reinserted). Rabbi Leibel Groner quite a few years ago asked the Rebbe about it and whether he could confirm the story. He did.
He then asked if he could publicize it and the Rebbe said yes. Yet Rabbi Groner never has, until now. His reason for not doing so at the time was because the Rebbe was then coming out with the call of We Want Mashiach Now and that at any moment Mashiach could come.
As such, he felt uncomfortable to publicize this story then. Now, it seems, as we approach 5775, he revealed this conversation he had with the Rebbe and is publicizing it finally.