yfere > together
2 Forth marched to a castle them before, 3 Where, soon arriving, they restrained were
restrained > deprived
4 Of ready entrance, which ought evermore 5 To errant knights be common: wondrous sore
errant > itinerant (a "knight errant" roamed in quest of quest of adventure; the word-order here also implies the sense of erring, deviating) common > generally accessible; hence: freely available
6 Thereat displeased they were, till that young squire
Thereat > Because of that, at that
7 Gan them inform the cause why that same door
Gan > Did cause > reason
8 Was shut to all which lodging did desire: 9 Which, to let you weet, will further time require.