"There are too many Shares running at the same time belonging to this account"
This error occurs when you have too many Shares scheduled at the same time in the same account. The reason behind this is that every account can only make a limited amount of queries per minute.
To avoid this error you can
Schedule the Shares at different times, just offsetting with a couple of minutes can help
Enable "Only share periods with updated data" on the Shares
Decrease the date range of the Share
Disable or delete unused Shares
"This Share contains a data source ... with too much data"
A data source in the Share contains too much data to be able to be shared. The data source likely exceeds our Fair usage policy for what amount of data is allowed per day.
To avoid this error you can either
"Edit configuration" of the data source in the Data Sources page to include less data (eg. fewer dimensions)
Exclude it by filtering out the data source from the Funnel Share