Even if the value in B5 was just a text string...
TEXT(B5;"dd.mm.yy") would NOT return a #Value! error.
It would simply return the exact same text string that exists in B5

I've only been able to produce the #Value! error with that formula if B5 actually contains the #Value! error.


Is it really this formula exactly that is returning #Value! ?
=TEXT(B5;"dd.mm.yy")

Or are you also doing some sort of math operation with the result of that function? like
=TEXT(B5;"dd.mm.yy")+10

Or maybe it's another cell that then refers to the cell with the TEXT formula that is doing some math and returning the #Value! error.