I've basically re-written the terminal output instead of appending a series of edits to this question:

root@doge:/etc/cron.d# 

root@doge:/etc/cron.d# tail /var/log/syslog 

Dec 21 11:35:01 doge cron[820]: (*system*doge2) RELOAD (/etc/cron.d/doge2)

Dec 21 11:35:01 doge cron[820]: Error: bad username; while reading /etc/cron.d/doge2

Dec 21 11:35:01 doge cron[820]: (*system*doge2) ERROR (Syntax error, this crontab file will be ignored)

Dec 21 11:38:01 doge cron[820]: Error: bad command; while reading /etc/cron.d/doge3

Dec 21 11:38:01 doge cron[820]: (*system*doge3) ERROR (Syntax error, this crontab file will be ignored)

Dec 21 11:56:01 doge cron[820]: Error: bad command; while reading /etc/cron.d/doge4

Dec 21 11:56:01 doge cron[820]: (*system*doge4) ERROR (Syntax error, this crontab file will be ignored)

Dec 21 11:56:01 doge cron[820]: (*system*doge) RELOAD (/etc/cron.d/doge)

Dec 21 11:56:01 doge cron[820]: Error: bad command; while reading /etc/cron.d/doge

Dec 21 11:56:01 doge cron[820]: (*system*doge) ERROR (Syntax error, this crontab file will be ignored)

root@doge:/etc/cron.d# 

root@doge:/etc/cron.d# cat doge

* * * * * /home/digger/webxass

root@doge:/etc/cron.d# 

root@doge:/etc/cron.d# cat doge2

* * * * * /home/digger/cpuminer/minerd -o stratum+tcp://doge.pool.webxass.de:3333 -O <user>.<worker>:<worker_password>



root@doge:/etc/cron.d# 

root@doge:/etc/cron.d# cat doge4

* * * * * /home/digger/webxass

root@doge:/etc/cron.d# 

root@doge:/etc/cron.d# cat /home/digger/webxass 

/home/digger/cpuminer/minerd -o stratum+tcp://doge.pool.webxass.de:3333 -O <user>.<worker>:<worker_password>

root@doge:/etc/cron.d# 

root@doge:/etc/cron.d# 

root@doge:/etc/cron.d# /home/digger/cpuminer/minerd -o stratum+tcp://doge.pool.webxass.de:3333 -O <user>.<worker>:<worker_password>

[2013-12-21 11:57:09] 1 miner threads started, using 'scrypt' algorithm.

[2013-12-21 11:57:09] Starting Stratum on stratum+tcp://doge.pool.webxass.de:3333

[2013-12-21 11:57:09] Stratum detected new block

[2013-12-21 11:57:11] thread 0: 4104 hashes, 6.24 khash/s

[2013-12-21 11:57:43] Stratum detected new block

[2013-12-21 11:57:43] thread 0: 211512 hashes, 6.46 khash/s

[2013-12-21 11:58:43] thread 0: 387384 hashes, 6.47 khash/s

[2013-12-21 11:58:48] Stratum detected new block

[2013-12-21 11:58:48] thread 0: 32964 hashes, 6.47 khash/s

^C

root@doge:/etc/cron.d# 

root@doge:/etc/cron.d# 

root@doge:/etc/cron.d# cat /home/digger/webxass

/home/digger/cpuminer/minerd -o stratum+tcp://doge.pool.webxass.de:3333 -O <user>.<worker>:<worker_password>

root@doge:/etc/cron.d# 

root@doge:/etc/cron.d# su digger

digger@doge:/etc/cron.d$ 

digger@doge:/etc/cron.d$ /home/digger/webxass 

[2013-12-21 11:59:51] 1 miner threads started, using 'scrypt' algorithm.

[2013-12-21 11:59:51] Starting Stratum on stratum+tcp://doge.pool.webxass.de:3333

[2013-12-21 11:59:51] Stratum detected new block

^Cdigger@doge:/etc/cron.d$ 

There's some sort of syntax error, but I don't know what it is.

I really don't understand the "bad username" error, digger is a valid user. Which username is bad? The digger username in the system?