Easy-to-Apply Remedies for QuickBooks Error H303 QuickBooks is a versatile application that offers two user modes: single-user and multi-user. Nevertheless, the program sometimes goes through specific glitches that are complicated to resolve. For example, QuickBooks Error H303 is an issue that occurs when the user tries to go from the single-user mode to the multi-user mode. A common problem in the H series of errors, this issue is a sign that there is a fault in your connectivity. A misconfiguration in the hosting settings is the primary reason why this error arises in the first place. Read below to find out more.