Using SQL 7 SP3 on NT 4 SP6.

Seems one of our developers is complaining that during the hourly trans log backup of a specific db, he has problems accessing it, either it being very slow, or coming up with a login failure altogether. Are there any known adverse db effects with backing up the trans log while the db is in use, or should I be looking elsewhere for the problem instead of blaming the backups?

Ed